US20120163484A1 - Method and processing arrangement for joint processing of uplink data - Google Patents
Method and processing arrangement for joint processing of uplink data Download PDFInfo
- Publication number
- US20120163484A1 US20120163484A1 US13/379,179 US201013379179A US2012163484A1 US 20120163484 A1 US20120163484 A1 US 20120163484A1 US 201013379179 A US201013379179 A US 201013379179A US 2012163484 A1 US2012163484 A1 US 2012163484A1
- Authority
- US
- United States
- Prior art keywords
- user equipment
- uplink data
- processing
- coordinated reception
- reception points
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Images
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/0001—Arrangements for dividing the transmission path
- H04L5/0014—Three-dimensional division
- H04L5/0023—Time-frequency-space
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B17/00—Monitoring; Testing
- H04B17/30—Monitoring; Testing of propagation channels
- H04B17/309—Measuring or estimating channel quality parameters
- H04B17/364—Delay profiles
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/0202—Channel estimation
- H04L25/0204—Channel estimation of multiple channels
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/0202—Channel estimation
- H04L25/024—Channel estimation channel estimation algorithms
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/0202—Channel estimation
- H04L25/024—Channel estimation channel estimation algorithms
- H04L25/0242—Channel estimation channel estimation algorithms using matrix methods
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2662—Symbol synchronisation
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/0001—Arrangements for dividing the transmission path
Definitions
- the invention relates to the field of signal processing in wireless communication systems, and, in particular, to joint processing of uplink data transmitted from user equipments to coordinated reception points in wireless communication systems.
- JP joint processing
- COMP uplink coordinated multi-point trans-missions
- BS base stations
- eNBs enhanced NodeBs
- 3GPP has defined two different cyclic prefixes (CP), a normal and an extended one.
- the length of the extended cyclic prefix can be configured to allow for a corresponding maximum difference of the timing offsets (delay spread) of the uplink radio signals received in the different reception points.
- using such an extended cyclic prefix has the disadvantage of generating an additional overhead, which reduces the achievable overall uplink throughput.
- With the normal cyclic prefix 14 OFDM symbols can be used for the transmission within one sub-frame of the duration of 1 ms.
- Using the extended cyclic prefix allows for only 12 OFDM symbols per sub-frame.
- Using the extended cyclic prefix instead of the conventional cyclic prefix thus results in a throughput reduction that amounts to about 20 percent.
- One aspect of the invention relates to a method for joint processing of uplink data transmitted from at least one user equipment to a plurality of coordinated reception points of a wireless communication system, the method comprising: estimating and preferably compensating for individual propagation delays of the uplink data transmitted from one of the user equipments to the coordinated reception points, and compensating for a timing difference between a propagation delay of a coordinated reception point which serves the user equipment and at least one propagation delay of at least one coordinated reception point which does not serve the user equipment for performing the joint processing of the uplink data, wherein the step of compensating the timing difference comprises modifying a channel matrix associated with uplink channels from the at least one user equipment to the coordinated reception points.
- each user equipment is served with downlink data from only one so-called “serving” reception point, a timing advance being provided for aligning the timing of the user equipment to its serving reception point (in the following also referred to as a cell).
- the propagation delay from a user equipment to its serving coordinated reception point may be compensated by adjusting, in the time domain, the position of a processing window for performing a time-to-frequency-domain transformation, in particular a Fast-Fourier-Transformation, FFT, on symbols of the uplink data.
- FFT Fast-Fourier-Transformation
- a dedicated timing delay/offset estimation within the layer1 processing of the serving cell may be used for this purpose.
- MIMO multiple-input-multiple-output
- the inventors propose to perform a timing offset estimation also in the non-serving cells of the coordination cluster in order to detect the correct timing of the sub-frames and OFDM symbols per user equipment.
- the difference in the timing offsets/propagation delays between different cells can be taken into account and can be used to modify the channel matrix (per sub-carrier, see below) associated with the uplink transmissions for taking the timing difference into account.
- joint processing may be performed even if the difference in the propagation delays from one user equipment to different reception points exceeds the length of the cyclic prefix being used in classical OFDMA-based systems.
- the step of modifying the channel matrix comprises performing a phase-shift on channel coefficients of the channel matrix associated with non-serving coordinated reception points.
- a modified MIMO channel matrix may be generated which compensates for the difference of the timing delays, thus allowing joint processing of the uplink data.
- the step of modifying the channel matrix further comprises modifying an amplitude of the channel coefficients of the channel matrix associated with the non-serving coordinated reception points, preferably by multiplying the channel coefficients with a real number smaller than one.
- the size of the processing window for performing a time-to-frequency domain transformation (FFT) on the user data from the non-serving reception points may be considerably reduced.
- the influence of the reduced size of the processing window may be taken into account by multiplying the corresponding channel coefficients of the channel matrix with a factor smaller than one, the factor depending on the size reduction of the FFT window.
- the uplink transmissions from the at least one user equipment to the coordinated reception points are performed in an orthogonal frequency division multiplex, OFDM, transmission scheme, an individual channel matrix being preferably defined for each sub-carrier of the OFDM transmission scheme.
- OFDM orthogonal frequency division multiplex
- an individual MIMO channel matrix is defined for each of the sub-carriers or for a group of sub-carriers used for the uplink transmission of the same user equipment.
- the method further comprises: performing a joint calculation of receiver antenna weights for the plurality of user equipments, the calculation being based on the modified cannel matrix.
- the modified MIMO channel matrix allows using a single receive combining set of antenna weights for all the antennas of the reception points, i.e. for the whole COMP cluster. It will be understood that several different receiver types may be used for performing the joint processing, for example receivers of the minimum mean-square error, MMSE, and/or successive interference cancellation, SIC, type.
- the uplink data is transferred from the coordinated reception points to a centralized unit for performing the joint processing, the uplink data being preferably transferred in the form of time domain or of frequency domain in-phase and quadrature-phase (IQ)-samples, in particular together with information about the propagation delay from each user equipment.
- IQ frequency domain in-phase and quadrature-phase
- the channel coefficients have to be exchanged between the base stations.
- the uplink data when transferring the uplink data as time domain IQ samples, the information about the timing offset is not required but may nevertheless be present, whereas when transferring frequency domain IQ samples, typically additional information about the propagation delay has to be transferred to the centralized unit.
- the uplink data may also be transferred to the centralized unit in another format, e.g. as soft bits or as decoded data.
- the joint processing comprises: performing a joint time-to-frequency domain transformation, in particular a Fast-Fourier-Transformation, FFT, on time domain samples of the uplink data of a plurality of user equipments having similar propagation delays to a common non-serving reception point.
- FFT Fast-Fourier-Transformation
- a further variant comprises choosing the repetition rate for estimating the propagation delay in dependence of the speed of movement of the user equipment.
- the rate for updating of the timing offset estimation may decrease with decreasing mobility of the (mobile) user equipment, i.e. updates have to be performed less often for slowly moving mobile stations than for rapidly moving mobile users.
- different types of user equipment with different mobility characteristics may be used in the wireless network, such as mobile phones, PDAs, Laptops, or also stationary equipment.
- the joint processing comprises: performing a Fast-Fourier-Transformation, FFT, on a number of time domain samples of the uplink data in a processing window, the method preferably further comprising: shifting the processing window by subtracting a discrete Fourier transform, DFT, contribution for each sub-carrier of one or more time domain samples at one end of the processing window and adding a discrete Fourier transform, DFT, contribution for each sub-carrier of a corresponding number of time domain samples at the other end of the processing window.
- DFT discrete Fourier transform
- the “processing window” is defined in the frequency domain for a parallel processing of a number of samples corresponding to adjacent sub-carriers of the OFDMA signal.
- the method as described above may also be realized in the form of a computer program product which may be implemented in a suitable software or hardware, in particular a field programmable gate array (FPGA), an application-specific integrated circuit (ASIC), or a digital signal processor (DSP).
- FPGA field programmable gate array
- ASIC application-specific integrated circuit
- DSP digital signal processor
- the computer program product may also comprise a plurality of separate parts which may be arranged at different locations.
- the method may in particular be implemented in a suitable software or hardware of a receiver for performing the joint processing, the latter possibly not performing the first step of estimating the propagation delays, as it may receive the information about the estimation from another physical entity together with samples of downlink data.
- a further aspect of the invention is implemented in a processing arrangement for joint processing of uplink data transmitted from at least one user equipment to a plurality of coordinated reception points of a wireless communication system, the processing arrangement being adapted to estimate and preferably to compensate for individual propagation delays of the uplink data transmitted from one of the user equipments to the coordinated reception points, the processing arrangement being further adapted to compensate for a timing difference between a propagation delay of a coordinated reception point which serves the user equipment and a propagation delay of at least one coordinated reception point which does not serve the user equipment for performing the joint processing of the uplink data, the processing arrangement being adapted to compensate for the timing difference by modifying a channel matrix associated with uplink channels from the at least one user equipment to the coordinated reception points.
- the processing arrangement as described above allows for performing COMP using joint detection without having to increase the length of the cyclic prefix, thus increasing the throughput. It will be understood that in the most simple case, the processing arrangement may be implemented as a receiver for performing the joint processing. However, it may also be possible that the estimation and compensation of the propagation delay to the serving reception point may be performed at a different location as the compensation of the timing difference to the non-serving cells.
- the processing arrangement is adapted for compensating the timing difference adapted for performing a phase-shift on channel coefficients of the channel matrix associated with non-serving coordinated reception points.
- the channel coefficients which are related to the non-serving reception points typically correspond to the non-diagonal elements of the MIMO channel matrix, whereas the diagonal elements of the MIMO channel matrix represent channels between the user equipment and a respective serving reception point.
- the processing arrangement is further adapted for modifying an amplitude of the channel coefficients of the channel matrix associated with the non-serving coordinated reception points, preferably by multiplying the channel coefficients by a real number smaller than one. As described above, in this way, the influence of a size reduction of a processing window for performing a FFT on the non-serving reception points may be taken into account.
- the processing arrangement is adapted to perform a joint calculation of receiver weights for the plurality of user equipments, the calculation being based on the modified channel matrix.
- the receiver weight matrix may be derived from the modified channel matrix by performing matrix calculations, as detailed further below.
- the uplink data is transmitted from the at least one user equipment to the coordinated reception points in an orthogonal frequency division multiplex, OFDM, transmission scheme, and the processing arrangement is preferably adapted to generate an individual channel matrix for each sub-carrier of the OFDM transmission scheme. In this way, the transmission properties for each sub-carrier of the frequency band of the ODFMA transmission scheme may be optimized individually.
- a further aspect is implemented in a base station comprising a processing arrangement as described above.
- the base station may comprise a central unit comprising a receiving device which is adapted for performing the joint processing of the uplink data.
- the reception points may e.g. be implemented as remote radio heads (RRHs) being arranged remotely from the central unit and serving different sectors of the base station, or the base station may be the serving reception point, the uplink data of further base stations, forming the non-serving coordinated reception points, being transferred to the serving base station e.g. via a backhaul network, the estimation of the propagation delays of the non-serving reception points being performed in the serving base station.
- RRHs remote radio heads
- the processing arrangement may comprise several physical entities which may be located at different positions within the network.
- the reception points may correspond to base stations which are connected via a common backhaul, e.g. packet-based (IP) network, the central unit being located in the backhaul network.
- IP packet-based
- the serving base station compensates for the propagation delay e.g. in the way described above, and that the propagation delay of the other base stations may be taken into account by an appropriate modification of the channel matrix.
- FIG. 1 shows a schematic diagram of an embodiment of a wireless communication network
- FIG. 2 shows a schematic diagram of uplink data from two user equipments received in one of the base stations of the network of FIG. 1 , and
- FIG. 3 shows a schematic diagram of the shifting of a FFT processing window in the frequency domain.
- FIG. 1 shows a wireless communication network 1 which may be in compliance with e.g. the Long-Term Evolution, LTE, standard, the WiMax standard, or another wireless communication standard.
- the wireless communication network 1 has a plurality of user equipments; however, for the sake of simplicity, only a first and second user equipment UE 1 , UE 2 are shown.
- the first user equipment UE 1 is served by a first base station BS A
- the second user equipment UE 2 is served by a second base station BS B of the network 1 , respectively.
- serving base station refers to the provisioning of downlink data from the respective base station BS A , BS B to the user equipment UE 1 , UE 2 , typically the serving base station being the one which is closest to the served user equipment.
- Each base station BS A , BS B defines a cell, being represented by a hexagon in FIG. 1 .
- the first and second user equipment UE 1 , UE 2 transmit their respective uplink data g(n), s(n) to both the first and to the second base station BS A , BS B , respectively.
- the base stations BS A , BS B thus form coordinated reception points for performing uplink coordinated multi-point transmission (COMP) and are operatively connected to a centralized unit 2 for performing joint processing (JP) of the uplink data, the centralized unit 2 being arranged at a remote location, e.g. in a (high-speed) data network.
- the first and second base stations BS A , BS B are coordinated, whereas a third base station BS C of the network 1 does not form part of the COMP coordination cluster as defined by the first and second base stations BS A , BS B .
- the coordinated reception points may be implemented as different sectors (corresponding e.g. to remote radio heads, RRHs) of the same base station, a backhaul processing unit of the base station serving as a centralized unit in this case (the propagation delays of the uplink signal in the sectors being different e.g. due to different multiple reflections.
- the base station BS A forms a centralized unit for performing joint processing of the uplink data g(n) from the first user equipment UE 1
- the second base station BS B is used as a centralized unit for joint processing of the uplink data s(n) from the second user equipment UE 2 .
- time synchronicity and frequency synchronicity of the base stations BS A , BS B and thus also frequency synchronicity of the uplink data g(n), s(n) will be assumed. Further, it will be assumed that in each base station BS A , BS B , the uplink data g(n), s(n) will be received in an individual time base which is aligned to the propagation delay of the user equipment UE 1 , UE 2 served by the respective base station BS A , BS B .
- the received signal r A (t) is represented in FIG. 2 , showing in the upper part OFDM symbols u 0 (n), u 1 (n), . . . of the uplink data g(n) from the first user equipment UE 1 which is served by the first base station BS A .
- the uplink data g(n), resp., the OFDM symbols u 0 (n), u 1 (n) are time-aligned to respective FFT processing window W 1 , covering only that part of the OFDM symbols u 0 (n), u 1 (n) which does not contain the cyclic prefix.
- the signal g(n) received from the served user equipment UE 1 is in its optimum position for decoding.
- An analogous time alignment is also performed for the uplink data s(n) of the second user equipment UE 2 which is received in the second base station BS B (the respective signal not being shown for the sake of simplicity).
- the lower part of FIG. 2 shows the OFDM symbols v ⁇ 1 (n), v 0 (n), . . . of the uplink data s(n) received from the second user equipment UE 2 in the first base station BS A .
- the uplink data g(n) of the first user equipment UE 1 is shifted by a timing difference with respect to the optimum position of the FFT window.
- the signal s(n) received from UE 2 depicted in the lower part of FIG. 2 will be analyzed.
- s 0 CP (n) is the transmit signal from the first user equipment UE 1 including a cyclic prefix.
- FFT window W 2 the result from the FFT would be
- the window function w(t) has to be taken into account.
- sub-carrier frequency f k i.e. the value V 0 (f k )
- S 0 (f k+1 ) and S 0 (f k+1 ) are relevant (cross-talk). So the decoupling that allowed that one sub-carrier frequency can be detected with a linear equation system in that sub-carrier frequency f k only, is no longer valid. Further, there is an additional influence from the previous OFDM symbol, that is from s ⁇ 1 (n), such that again, there is a coupling in time-direction between the symbols.
- the uplink COMP joint processing system 1 which is exemplarily illustrated in FIG. 1 may be regarded as a composite MIMO system with an associated channel matrix H, having a dimension corresponding to the number of receiver antennas times the number of transmitter antennas, being a 2 ⁇ 2 matrix in the present (simplified) example with two user equipments UE 1 , UE 2 serving as transmitters and two base stations BS A , BS B serving as receivers (and supposing that each of these is only equipped with a single antenna).
- the channel matrix H is given by:
- first row vector h 1A , h 2A is related to the first uplink data g(n) transmitted from the first user equipment UE 1 to the first and second base station BS A , BS B , respectively
- second row vector h 1B , h 2B is related to second uplink data s(n), being transmitted from the second user equipment UE 2 to the first and second base stations BS A , BS B .
- the wireless communication network 1 more precisely the user equipments UE 1 , UE 2 and the base stations BS A , BS B , are adapted for performing uplink transmissions in an orthogonal frequency division multiplex, OFDM, transmission scheme, dividing the frequency band reserved for the uplink transmission into a plurality of orthogonal sub-carriers.
- OFDM orthogonal frequency division multiplex
- an individual channel matrix H may be defined for each sub-carrier (or for a group of sub-carriers).
- a receiver in the centralized unit 2 will jointly process the uplink data g(n), s(n) from the user equipments UE 1 and UE 2 and may e.g. be devised as a linear Minimum Mean Square Error, MMSE, receiver which calculates its weight matrix
- the first row vector of the weight matrix G is the complex antenna weight set used to decode the first uplink data g(n) received from the first user equipment UE 1
- the second row vector is the antenna weight set used to decode the second uplink data s(n) received from the second user equipment UE 2 .
- the formula for the calculation of the weight matrix G in dependence of the channel matrix H for the MMSE receiver is given as follows:
- G MMSE ( H H H+ ⁇ n 2 I ) ⁇ 1 H H ,
- ⁇ n is the standard deviation of the Gaussian noise due to the transmission
- I designates the identity matrix
- a timing advance for the propagation delay of the uplink data g(n) to first user equipment UE 1 may be implemented in the serving base station BS A by shifting the processing window W 1 of the time-to-frequency transformation (FFT) accordingly, for example by using a timing offset estimation within the layer1 processing of the serving base station BS A .
- a timing advance may be performed for the second uplink data s(n) being received in the second base station BS B serving the second user equipment UE 2 .
- the above formula for calculating the receiver weight matrix G is however only valid when both user equipments UE 1 , UE 2 are processed on a common time basis, using a joint Fast-Fourier-Transform.
- the user equipment UE 1 has a different distance to the first and to the second base station BS A , BS B , respectively, and the propagation delay of the uplink data g(n) from the first user equipment UE 1 to the first and second base station BS A , BS B will be different.
- This problem may be mitigated in an OFDMA transmission system by using an (extended) cyclic prefix that is large enough for the multi-path propagation plus additional propagation differences of the multi-cell COMP system 1 .
- an extended prefix that is large enough for the multi-path propagation plus additional propagation differences of the multi-cell COMP system 1 .
- using such an extended prefix will increase the overhead and thus reduce the throughput of the system.
- the timing for each user equipment UE 1 , UE 2 to its own serving base station BS A , BS B is controlled by the timing advance in the way described above.
- a separate timing offset/propagation delay estimation is performed and their FFT processing window may be shifted by a corresponding amount in order to be aligned with the individual symbol borders of the user equipments UE 1 , UE 2 .
- the modified channel matrix H mod may then be used for calculating the complex weight matrix G in the centralized unit 2 (see below), the inter-symbol interference being treated as noise.
- the uplink data s(n), g(n) may be transferred in the form of time domain (IQ) samples to the centralized unit 2 .
- IQ samples correspond to the Quadrature Phase-Shift Keying (QPSK) modulation format, but that other modulation formats may be used as well.
- the timing offset estimation may be performed e.g. in the centralized unit 2 .
- each base station may perform a timing offset estimation for searched user equipments and a calculation of the channel coefficients (in the UE-specific time-base) on its own, and also perform the calculation of the modified channel matrix.
- the uplink data may be transferred as frequency domain IQ samples, in the form of soft bits or as decoded data to the centralized unit 2 . It will be understood that in any case, the uplink data UD 1 , UD 2 may be transferred to the centralized unit 2 together with information about the timing offset/propagation delay.
- the steps for multi-user detection may be as follows:
- a single joint FFT may be performed for a set of user equipments which have roughly the same propagation delays to the non-serving base station, resp. cell.
- the user equipments may be grouped into different sets, each set comprising only user equipments having similar propagation delay.
- a further approach for complexity reduction may be to update the timing offset estimation (and optionally the grouping as described above) in dependence of the velocity of the user equipments: For slowly moving mobile stations, updates have to be performed less often than for high-speed mobile stations.
- a further complexity reduction by reducing the number of necessary FFTs may be achieved in the following way: After a FFT has been performed for a set of time domain samples, e.g. samples a 0 to a 5 being related to different sub-carriers in a processing window W in the frequency domain, as shown in FIG.
- N the number of sub-carriers for which the processing window is defined.
- uplink coordinated multi-point transmissions may be performed without having to enlarge the cyclic prefix of the OFDMA scheme.
- Using the above approach thus avoids increasing the overhead due to such a cyclic prefix extension, thus increasing the spectral efficiency of the COMP scheme.
- the approach described above may also be used in transmission schemes being derived from the OFDMA scheme, for example in the so-called Single-Carrier Frequency Division Multiple Access, SC-FDMA, transmission scheme, being a linear pre-coded OFDMA scheme.
Landscapes
- Engineering & Computer Science (AREA)
- Signal Processing (AREA)
- Computer Networks & Wireless Communication (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- Quality & Reliability (AREA)
- Electromagnetism (AREA)
- Mathematical Physics (AREA)
- Mobile Radio Communication Systems (AREA)
Abstract
Description
- The invention relates to the field of signal processing in wireless communication systems, and, in particular, to joint processing of uplink data transmitted from user equipments to coordinated reception points in wireless communication systems.
- This section introduces aspects that may be helpful in facilitating a better understanding of the invention. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
- When performing joint processing (JP) of uplink coordinated multi-point trans-missions (so-called COMP), one has to deal with multi-path propagations leading to different timing/propagation delays to the different reception points (e.g. base stations) of a COMP coordination cluster. If the difference of the timing offsets due to the different propagation delays exceeds the length reserved for the cyclic prefix in an Orthogonal Frequency Division Multiplex, OFDM, transmission scheme, the joint processing of the uplink signals of different COMP reception points (for example located in different base stations (BS), such as enhanced NodeBs “eNBs”) in a single receiver is no longer possible.
- For this reason 3GPP has defined two different cyclic prefixes (CP), a normal and an extended one. To allow for joint processing, the length of the extended cyclic prefix can be configured to allow for a corresponding maximum difference of the timing offsets (delay spread) of the uplink radio signals received in the different reception points. However, using such an extended cyclic prefix has the disadvantage of generating an additional overhead, which reduces the achievable overall uplink throughput. With the normal cyclic prefix, 14 OFDM symbols can be used for the transmission within one sub-frame of the duration of 1 ms. Using the extended cyclic prefix allows for only 12 OFDM symbols per sub-frame. Using the extended cyclic prefix instead of the conventional cyclic prefix thus results in a throughput reduction that amounts to about 20 percent.
- One aspect of the invention relates to a method for joint processing of uplink data transmitted from at least one user equipment to a plurality of coordinated reception points of a wireless communication system, the method comprising: estimating and preferably compensating for individual propagation delays of the uplink data transmitted from one of the user equipments to the coordinated reception points, and compensating for a timing difference between a propagation delay of a coordinated reception point which serves the user equipment and at least one propagation delay of at least one coordinated reception point which does not serve the user equipment for performing the joint processing of the uplink data, wherein the step of compensating the timing difference comprises modifying a channel matrix associated with uplink channels from the at least one user equipment to the coordinated reception points.
- Typically, each user equipment is served with downlink data from only one so-called “serving” reception point, a timing advance being provided for aligning the timing of the user equipment to its serving reception point (in the following also referred to as a cell). Thus, the propagation delay from a user equipment to its serving coordinated reception point may be compensated by adjusting, in the time domain, the position of a processing window for performing a time-to-frequency-domain transformation, in particular a Fast-Fourier-Transformation, FFT, on symbols of the uplink data. A dedicated timing delay/offset estimation within the layer1 processing of the serving cell may be used for this purpose. However, when multiple user equipments have to be detected on the same multiple access (time/frequency/code) resource over several cells by multiple-input-multiple-output (MIMO) receiver strategies/multi-user detection, the problem occurs that the timing of the cells may be different.
- For overcoming this problem, the inventors propose to perform a timing offset estimation also in the non-serving cells of the coordination cluster in order to detect the correct timing of the sub-frames and OFDM symbols per user equipment. Thus, the difference in the timing offsets/propagation delays between different cells can be taken into account and can be used to modify the channel matrix (per sub-carrier, see below) associated with the uplink transmissions for taking the timing difference into account. In such a way, joint processing may be performed even if the difference in the propagation delays from one user equipment to different reception points exceeds the length of the cyclic prefix being used in classical OFDMA-based systems. As this solution compensates the propagation delay differences of COMP cells, a type of cyclic prefix can be used that is appropriate for the multi-path propagation conditions, disregarding the timing offset to the non-serving COMP reception points. Hence, there is no need to increase the overhead when applying the COMP reception scheme.
- In one variant, the step of modifying the channel matrix comprises performing a phase-shift on channel coefficients of the channel matrix associated with non-serving coordinated reception points. By multiplying the phase into the MIMO channel matrix of the composite COMP MIMO channel, a modified MIMO channel matrix may be generated which compensates for the difference of the timing delays, thus allowing joint processing of the uplink data.
- In an improvement of this variant, the step of modifying the channel matrix further comprises modifying an amplitude of the channel coefficients of the channel matrix associated with the non-serving coordinated reception points, preferably by multiplying the channel coefficients with a real number smaller than one. In particular when the difference between the propagation delays of different reception points is large, the size of the processing window for performing a time-to-frequency domain transformation (FFT) on the user data from the non-serving reception points may be considerably reduced. The influence of the reduced size of the processing window may be taken into account by multiplying the corresponding channel coefficients of the channel matrix with a factor smaller than one, the factor depending on the size reduction of the FFT window.
- In a further variant, the uplink transmissions from the at least one user equipment to the coordinated reception points are performed in an orthogonal frequency division multiplex, OFDM, transmission scheme, an individual channel matrix being preferably defined for each sub-carrier of the OFDM transmission scheme. When using such a transmission scheme, typically, an individual MIMO channel matrix is defined for each of the sub-carriers or for a group of sub-carriers used for the uplink transmission of the same user equipment.
- In one improvement the method further comprises: performing a joint calculation of receiver antenna weights for the plurality of user equipments, the calculation being based on the modified cannel matrix. The modified MIMO channel matrix allows using a single receive combining set of antenna weights for all the antennas of the reception points, i.e. for the whole COMP cluster. It will be understood that several different receiver types may be used for performing the joint processing, for example receivers of the minimum mean-square error, MMSE, and/or successive interference cancellation, SIC, type.
- In a further variant, the uplink data is transferred from the coordinated reception points to a centralized unit for performing the joint processing, the uplink data being preferably transferred in the form of time domain or of frequency domain in-phase and quadrature-phase (IQ)-samples, in particular together with information about the propagation delay from each user equipment. In case of frequency domain IQ-samples, also the channel coefficients have to be exchanged between the base stations. When each user on its individual time-base (creating one FFT per user equipment and performing COMP in a non-serving cell with individually matched timing) is detected, the frequency domain IQ samples or soft bits can be transported over the backhaul to a central point (usually the base station of the serving cell) for performing the joint processing of the coordinated multipoint reception. It will be understood that when transferring the uplink data as time domain IQ samples, the information about the timing offset is not required but may nevertheless be present, whereas when transferring frequency domain IQ samples, typically additional information about the propagation delay has to be transferred to the centralized unit. Of course, the uplink data may also be transferred to the centralized unit in another format, e.g. as soft bits or as decoded data.
- In a further variant, the joint processing comprises: performing a joint time-to-frequency domain transformation, in particular a Fast-Fourier-Transformation, FFT, on time domain samples of the uplink data of a plurality of user equipments having similar propagation delays to a common non-serving reception point. When two or more user equipments are present which have a similar distance from the same reception point, a joint FFT may be performed for transforming time domain samples of the uplink data to frequency domain samples, thus reducing the overall number of FFTs being required for this purpose, and consequently also the complexity of the calculations. It will be understood that for this purpose, typically the user equipments will be grouped into different sets, each having a similar propagation delay.
- A further variant comprises choosing the repetition rate for estimating the propagation delay in dependence of the speed of movement of the user equipment. In particular, the rate for updating of the timing offset estimation (and optionally the grouping as described above) may decrease with decreasing mobility of the (mobile) user equipment, i.e. updates have to be performed less often for slowly moving mobile stations than for rapidly moving mobile users. One skilled in the art will appreciate that different types of user equipment with different mobility characteristics may be used in the wireless network, such as mobile phones, PDAs, Laptops, or also stationary equipment.
- In one improvement, the joint processing comprises: performing a Fast-Fourier-Transformation, FFT, on a number of time domain samples of the uplink data in a processing window, the method preferably further comprising: shifting the processing window by subtracting a discrete Fourier transform, DFT, contribution for each sub-carrier of one or more time domain samples at one end of the processing window and adding a discrete Fourier transform, DFT, contribution for each sub-carrier of a corresponding number of time domain samples at the other end of the processing window. One skilled in the art will readily recognize that in the present case, the “processing window” is defined in the frequency domain for a parallel processing of a number of samples corresponding to adjacent sub-carriers of the OFDMA signal.
- In the way described above, a further reduction of the number of necessary FFTs for an OFDMA transmission scheme can be performed, as follows: For processing a new set of samples having a FFT window which is just shifted (in the frequency domain) by one or by several samples with respect to a previously processed set of samples, instead of processing a new FFT for the new set of samples, it is proposed to add the DFT contribution per sub-carrier of the one or more new sample values at one end of the FFT window and to subtract the first sample value(s) of the previous FFT window. This concept can also be combined with the concepts described above, e.g. first grouping the user equipments according to their propagation delays, doing a FFT for each of the groups and shifting the FFT window in the above-described manner until all the user equipments of a particular group are covered, thus possibly requiring to perform only one FFT for each group of user equipments.
- One skilled in the art will appreciate that the method as described above may also be realized in the form of a computer program product which may be implemented in a suitable software or hardware, in particular a field programmable gate array (FPGA), an application-specific integrated circuit (ASIC), or a digital signal processor (DSP). Of course, the computer program product may also comprise a plurality of separate parts which may be arranged at different locations. It will be understood that the method may in particular be implemented in a suitable software or hardware of a receiver for performing the joint processing, the latter possibly not performing the first step of estimating the propagation delays, as it may receive the information about the estimation from another physical entity together with samples of downlink data.
- A further aspect of the invention is implemented in a processing arrangement for joint processing of uplink data transmitted from at least one user equipment to a plurality of coordinated reception points of a wireless communication system, the processing arrangement being adapted to estimate and preferably to compensate for individual propagation delays of the uplink data transmitted from one of the user equipments to the coordinated reception points, the processing arrangement being further adapted to compensate for a timing difference between a propagation delay of a coordinated reception point which serves the user equipment and a propagation delay of at least one coordinated reception point which does not serve the user equipment for performing the joint processing of the uplink data, the processing arrangement being adapted to compensate for the timing difference by modifying a channel matrix associated with uplink channels from the at least one user equipment to the coordinated reception points.
- The processing arrangement as described above allows for performing COMP using joint detection without having to increase the length of the cyclic prefix, thus increasing the throughput. It will be understood that in the most simple case, the processing arrangement may be implemented as a receiver for performing the joint processing. However, it may also be possible that the estimation and compensation of the propagation delay to the serving reception point may be performed at a different location as the compensation of the timing difference to the non-serving cells.
- In one embodiment, the processing arrangement is adapted for compensating the timing difference adapted for performing a phase-shift on channel coefficients of the channel matrix associated with non-serving coordinated reception points. The channel coefficients which are related to the non-serving reception points typically correspond to the non-diagonal elements of the MIMO channel matrix, whereas the diagonal elements of the MIMO channel matrix represent channels between the user equipment and a respective serving reception point.
- In one improvement, the processing arrangement is further adapted for modifying an amplitude of the channel coefficients of the channel matrix associated with the non-serving coordinated reception points, preferably by multiplying the channel coefficients by a real number smaller than one. As described above, in this way, the influence of a size reduction of a processing window for performing a FFT on the non-serving reception points may be taken into account.
- In one improvement, the processing arrangement is adapted to perform a joint calculation of receiver weights for the plurality of user equipments, the calculation being based on the modified channel matrix. The receiver weight matrix may be derived from the modified channel matrix by performing matrix calculations, as detailed further below.
- In a further embodiment, the uplink data is transmitted from the at least one user equipment to the coordinated reception points in an orthogonal frequency division multiplex, OFDM, transmission scheme, and the processing arrangement is preferably adapted to generate an individual channel matrix for each sub-carrier of the OFDM transmission scheme. In this way, the transmission properties for each sub-carrier of the frequency band of the ODFMA transmission scheme may be optimized individually.
- A further aspect is implemented in a base station comprising a processing arrangement as described above. The base station may comprise a central unit comprising a receiving device which is adapted for performing the joint processing of the uplink data. In this case, the reception points may e.g. be implemented as remote radio heads (RRHs) being arranged remotely from the central unit and serving different sectors of the base station, or the base station may be the serving reception point, the uplink data of further base stations, forming the non-serving coordinated reception points, being transferred to the serving base station e.g. via a backhaul network, the estimation of the propagation delays of the non-serving reception points being performed in the serving base station.
- Yet another aspect is implemented in a wireless communication network comprising at least one processing arrangement as described above. In this case, the processing arrangement may comprise several physical entities which may be located at different positions within the network. For example, the reception points may correspond to base stations which are connected via a common backhaul, e.g. packet-based (IP) network, the central unit being located in the backhaul network. It may also be possible to transfer uplink data from the non-serving reception points being located e.g. at different base stations, to the serving reception point (serving base station), the serving base station then performing the joint processing for the user equipment. It will be understood that typically, the serving base station compensates for the propagation delay e.g. in the way described above, and that the propagation delay of the other base stations may be taken into account by an appropriate modification of the channel matrix.
- Further features and advantages are stated in the following description of exemplary embodiments, with reference to the figures of the drawing, which shows significant details, and are defined by the claims. The individual features can be implemented individually by themselves, or several of them can be implemented in any desired combination.
- Exemplary embodiments are shown in the diagrammatic drawing and are explained in the description below. The following are shown:
-
FIG. 1 shows a schematic diagram of an embodiment of a wireless communication network, -
FIG. 2 shows a schematic diagram of uplink data from two user equipments received in one of the base stations of the network ofFIG. 1 , and -
FIG. 3 shows a schematic diagram of the shifting of a FFT processing window in the frequency domain. -
FIG. 1 shows a wireless communication network 1 which may be in compliance with e.g. the Long-Term Evolution, LTE, standard, the WiMax standard, or another wireless communication standard. The wireless communication network 1 has a plurality of user equipments; however, for the sake of simplicity, only a first and second user equipment UE1, UE2 are shown. The first user equipment UE1 is served by a first base station BSA, and the second user equipment UE2 is served by a second base station BSB of the network 1, respectively. The term “serving” base station refers to the provisioning of downlink data from the respective base station BSA, BSB to the user equipment UE1, UE2, typically the serving base station being the one which is closest to the served user equipment. Each base station BSA, BSB defines a cell, being represented by a hexagon inFIG. 1 . - The first and second user equipment UE1, UE2 transmit their respective uplink data g(n), s(n) to both the first and to the second base station BSA, BSB, respectively. The base stations BSA, BSB thus form coordinated reception points for performing uplink coordinated multi-point transmission (COMP) and are operatively connected to a
centralized unit 2 for performing joint processing (JP) of the uplink data, thecentralized unit 2 being arranged at a remote location, e.g. in a (high-speed) data network. Thus, the first and second base stations BSA, BSB are coordinated, whereas a third base station BSC of the network 1 does not form part of the COMP coordination cluster as defined by the first and second base stations BSA, BSB. - One skilled in the art will appreciate that alternatively, the coordinated reception points may be implemented as different sectors (corresponding e.g. to remote radio heads, RRHs) of the same base station, a backhaul processing unit of the base station serving as a centralized unit in this case (the propagation delays of the uplink signal in the sectors being different e.g. due to different multiple reflections.
- It will be understood that, instead of performing the joint processing in the
centralized unit 2, it is also possible to perform the joint processing of the uplink data originating from one user equipment in its serving base station or cell, respectively. In this case, the data of the at least one non-serving base station will be transferred to the serving base station, e.g. over a cable connection, a data network, etc. as indicated by a dashed line inFIG. 1 . In the latter case, the base station BSA forms a centralized unit for performing joint processing of the uplink data g(n) from the first user equipment UE1, and the second base station BSB is used as a centralized unit for joint processing of the uplink data s(n) from the second user equipment UE2. - In the following, time synchronicity and frequency synchronicity of the base stations BSA, BSB and thus also frequency synchronicity of the uplink data g(n), s(n) will be assumed. Further, it will be assumed that in each base station BSA, BSB, the uplink data g(n), s(n) will be received in an individual time base which is aligned to the propagation delay of the user equipment UE1, UE2 served by the respective base station BSA, BSB.
- For the first base station BSA, the received signal rA(t) is represented in
FIG. 2 , showing in the upper part OFDM symbols u0(n), u1(n), . . . of the uplink data g(n) from the first user equipment UE1 which is served by the first base station BSA. The uplink data g(n), resp., the OFDM symbols u0(n), u1(n) are time-aligned to respective FFT processing window W1, covering only that part of the OFDM symbols u0(n), u1(n) which does not contain the cyclic prefix. Thus, the signal g(n) received from the served user equipment UE1 is in its optimum position for decoding. An analogous time alignment is also performed for the uplink data s(n) of the second user equipment UE2 which is received in the second base station BSB (the respective signal not being shown for the sake of simplicity). - The lower part of
FIG. 2 shows the OFDM symbols v−1(n), v0(n), . . . of the uplink data s(n) received from the second user equipment UE2 in the first base station BSA. As can be seen fromFIG. 2 , the position of a FFT processing window W2 for processing the uplink data s(n) is shifted by a timing difference τ=t1−t2, the latter being due to the different propagation delays from the first and second user equipment UE1, UE2 to the first base station BSA. In a similar way, the uplink data g(n) of the first user equipment UE1 is shifted by a timing difference with respect to the optimum position of the FFT window. Consequently, when performing joint processing of uplink data g(n), s(n) received in a common FFT window which is time-aligned to the serving base station BSA, BSB, the influence of the time shift of the signal g(n), s(n) received in the non-serving base station BSB, BSA has to be taken into account. - In the following, with reference to
FIG. 2 , the steps will be given to calculate the influence of the signal s(n) in OFDM symbol s0(n) or of the respective sub-carrier complex amplitude S0(f=fk) at sub-carrier frequency fk on the FFT window W1 if no time shifts of the receive signals rA(t) at base station BSA (or rB(t) at base station BSB) are performed. For this purpose, the signal s(n) received from UE2 depicted in the lower part ofFIG. 2 will be analyzed. - If one looks at the signal s(n) in a time-base starting at t2, the signal is described by
-
s 0 CP(n)*h 2A(n)=v 0(n), - where s0 CP(n) is the transmit signal from the first user equipment UE1 including a cyclic prefix. In FFT window W2 the result from the FFT would be
-
S 0(ƒ)·H 2A(ƒ). - However, when performing a FFT on the signal s(n) using the FFT window W1, the window function w(t) has to be taken into account. First, there is the problem that not all sinusoids are contiguously in the window w(t) (which introduces cross talk between the frequencies of S0(f)). Second, even if this would be the case, still because of the time windowing by w(t), in the frequency domain there occurs a convolution with a window function W(f). If one ignores the discontinuity in the time-base starting at t2, the windowed result is:
-
- Then, the result from (that in FFT window W1 is
-
V 0(ƒ)≈{[S 0(ƒ)H 2A(ƒ)]*W τ(ƒ)}e −j2πƒτ. - Thus, for sub-carrier frequency fk, i.e. the value V0(fk), not only the transmitted sub-carrier amplitude S0(fk), but also S0(fk+1) and S0(fk+1) are relevant (cross-talk). So the decoupling that allowed that one sub-carrier frequency can be detected with a linear equation system in that sub-carrier frequency fk only, is no longer valid. Further, there is an additional influence from the previous OFDM symbol, that is from s−1(n), such that again, there is a coupling in time-direction between the symbols.
- If one ignores also this coupling and models the previous OFDM symbol part as noise, cross-talk over neighboring sub-carriers is still present. If one also wants to ignore this frequency coupling, one has for the resulting coefficients in FFT window W1:
-
[S 0(ƒk)H 2A(ƒk)]·W τ(ƒ=0)e −j2πƒk τ. - That is, there is not only a phase factor but due to the windowing with partial size there is also an amplitude change with a real factor Wτ(f=0)<1. This contribution needs to be taken into account especially for larger shifts. It may also influence the rank of the derived matrix that needs to be inverted, e.g. for use in a MMSE reception algorithm, which will be detailed in the following.
- The uplink COMP joint processing system 1 which is exemplarily illustrated in
FIG. 1 may be regarded as a composite MIMO system with an associated channel matrix H, having a dimension corresponding to the number of receiver antennas times the number of transmitter antennas, being a 2×2 matrix in the present (simplified) example with two user equipments UE1, UE2 serving as transmitters and two base stations BSA, BSB serving as receivers (and supposing that each of these is only equipped with a single antenna). Thus, in the present example, the channel matrix H is given by: -
- wherein the first row vector h1A, h2A is related to the first uplink data g(n) transmitted from the first user equipment UE1 to the first and second base station BSA, BSB, respectively, and the second row vector h1B, h2B is related to second uplink data s(n), being transmitted from the second user equipment UE2 to the first and second base stations BSA, BSB.
- In the present example, the wireless communication network 1, more precisely the user equipments UE1, UE2 and the base stations BSA, BSB, are adapted for performing uplink transmissions in an orthogonal frequency division multiplex, OFDM, transmission scheme, dividing the frequency band reserved for the uplink transmission into a plurality of orthogonal sub-carriers. For such an OFDMA transmission scheme, an individual channel matrix H may be defined for each sub-carrier (or for a group of sub-carriers).
- A receiver in the
centralized unit 2 will jointly process the uplink data g(n), s(n) from the user equipments UE1 and UE2 and may e.g. be devised as a linear Minimum Mean Square Error, MMSE, receiver which calculates its weight matrix -
- as a function of the channel matrix H (see below). The first row vector of the weight matrix G is the complex antenna weight set used to decode the first uplink data g(n) received from the first user equipment UE1, the second row vector is the antenna weight set used to decode the second uplink data s(n) received from the second user equipment UE2. The formula for the calculation of the weight matrix G in dependence of the channel matrix H for the MMSE receiver is given as follows:
-
G MMSE=(H H H+σ n 2 I)−1 H H, - wherein HH=H*T is the Hermitian conjugate of the matrix H, σn is the standard deviation of the Gaussian noise due to the transmission, an the letter I designates the identity matrix.
- As described above, a timing advance for the propagation delay of the uplink data g(n) to first user equipment UE1 may be implemented in the serving base station BSA by shifting the processing window W1 of the time-to-frequency transformation (FFT) accordingly, for example by using a timing offset estimation within the layer1 processing of the serving base station BSA. Likewise, a timing advance may be performed for the second uplink data s(n) being received in the second base station BSB serving the second user equipment UE2.
- The above formula for calculating the receiver weight matrix G is however only valid when both user equipments UE1, UE2 are processed on a common time basis, using a joint Fast-Fourier-Transform. However, as outlined above, the user equipment UE1 has a different distance to the first and to the second base station BSA, BSB, respectively, and the propagation delay of the uplink data g(n) from the first user equipment UE1 to the first and second base station BSA, BSB will be different.
- Thus, when multiple user equipments shall be detected on the same multiple access (time/frequency/code) resource over several base stations BSA, BSB by MIMO receiver strategies/multi-user detection, the problem occurs that the timing between the uplink signals g(n), s(n) being received in the different base stations BSA, BSB is completely different.
- This problem may be mitigated in an OFDMA transmission system by using an (extended) cyclic prefix that is large enough for the multi-path propagation plus additional propagation differences of the multi-cell COMP system 1. However, using such an extended prefix will increase the overhead and thus reduce the throughput of the system.
- In order to avoid such an (extended) cyclic prefix, the timing for each user equipment UE1, UE2 to its own serving base station BSA, BSB is controlled by the timing advance in the way described above. For the uplink signals g(n), s(n) from the user equipment UE1, UE2 which are received in the respective non-serving base stations BSB, BSA, a separate timing offset/propagation delay estimation is performed and their FFT processing window may be shifted by a corresponding amount in order to be aligned with the individual symbol borders of the user equipments UE1, UE2.
- However, the different additional (uncontrolled) propagation delays to non-serving base stations BSB, BSA for the first and second user equipment UE1 and UE2 have to be taken into account. The derivations above now allow one to define a modified channel matrix:
-
- The modified channel matrix Hmod may then be used for calculating the complex weight matrix G in the centralized unit 2 (see below), the inter-symbol interference being treated as noise.
- For the aggregation of the uplink data s(n), g(n) from the different coordinated reception points BSA, BSB to the centralized unit 2 (coordinator), several options exist: For example, the uplink data s(n), g(n) may be transferred in the form of time domain (IQ) samples to the
centralized unit 2. One skilled in the art will appreciate that IQ samples correspond to the Quadrature Phase-Shift Keying (QPSK) modulation format, but that other modulation formats may be used as well. - The timing offset estimation may be performed e.g. in the
centralized unit 2. Alternatively, each base station may perform a timing offset estimation for searched user equipments and a calculation of the channel coefficients (in the UE-specific time-base) on its own, and also perform the calculation of the modified channel matrix. - Alternatively, the uplink data may be transferred as frequency domain IQ samples, in the form of soft bits or as decoded data to the
centralized unit 2. It will be understood that in any case, the uplink data UD1, UD2 may be transferred to thecentralized unit 2 together with information about the timing offset/propagation delay. - In particular, when frequency domain IQ samples are transferred, the steps for multi-user detection may be as follows:
-
- a) In each cell the served user equipments are time-adjusted by TA (timing advance) commands,
- b) for non-served user equipments, the timing is estimated to find the UE time base. FFTs are performed for doing the channel estimation based on demodulation reference symbols, DM RS, in this shifted time base. The result is the set of channel coefficients per sub-carrier for this timing, and
- c) the frequency domain I/Q samples from FFTs of the original time base are exchanged together with non-served UE's timing information and channel coefficient information for these UEs, such that the receiving base station can then calculate the modified channel matrix.
- Thus, for an optimized performance of a centralized weight processing in the
centralized unit 2, it is proposed to transfer the uplink data in the form of time or frequency IQ samples, taking into account the timing offset and the corresponding phase shift per sub-carrier in the updated channel matrix Hmod, and processing the receiver weights according to: -
G MMSE=(H mod H H mod+σn 2 I)−1 H mod H, - i.e. by replacing the channel matrix H by the modified channel matrix Hmod.
- Those skilled in the art will appreciate that although the approach for calculating the weight matrix G in dependence of the modified channel matrix Hmod has been described for the example of a MMSE receiver, this approach is not limited to a specific receiver type, and may also be applied to other receiver types.
- In the following, several ways for reducing the computational complexity of the present approach will be explained, the computational complexity in particular being reduced by reducing the number of FFTs required for performing the time-to-frequency transformation of the time domain samples of the uplink data.
- First, a single joint FFT may be performed for a set of user equipments which have roughly the same propagation delays to the non-serving base station, resp. cell. For that purpose, the user equipments may be grouped into different sets, each set comprising only user equipments having similar propagation delay.
- A further approach for complexity reduction may be to update the timing offset estimation (and optionally the grouping as described above) in dependence of the velocity of the user equipments: For slowly moving mobile stations, updates have to be performed less often than for high-speed mobile stations.
- A further complexity reduction by reducing the number of necessary FFTs may be achieved in the following way: After a FFT has been performed for a set of time domain samples, e.g. samples a0 to a5 being related to different sub-carriers in a processing window W in the frequency domain, as shown in
FIG. 3 , instead of performing another FFT for a processing window W′ being shifted by two neighbouring time domain samples a6, a7, it is proposed to add the DFT(discrete Fourier transform) contribution per sub-carrier of the two new sample values a6, a7 from the DFT sum and to subtract the first two sample values a0, a1 from the DFT sum, thus resulting in the processing of the samples a2 to a7 in the shifted processing window W′. - The above approach is based on the fact that the DFT sum for the time-to-frequency domain transformed sample âk of the k-th sub-carrier of the OFDMA scheme can be written as:
-
- with k=0, . . . , N−1; wherein N represents the number of sub-carriers for which the processing window is defined.
- One skilled in the art will appreciate that using such an approach may result in performing only a few FFTs and shifting the processing window in the above-described manner for generating the other frequency domain samples âk. For instance, it may be possible to group the user equipments UE1, UE2 according to their propagation delays, to perform a FFT for each group of user equipments UE1, UE2 and to shift the FFT window in the way described above until all of the user equipments of a particular group are covered.
- In summary, by applying the approach described above, uplink coordinated multi-point transmissions may be performed without having to enlarge the cyclic prefix of the OFDMA scheme. Using the above approach thus avoids increasing the overhead due to such a cyclic prefix extension, thus increasing the spectral efficiency of the COMP scheme. It will be readily understood that the approach described above may also be used in transmission schemes being derived from the OFDMA scheme, for example in the so-called Single-Carrier Frequency Division Multiple Access, SC-FDMA, transmission scheme, being a linear pre-coded OFDMA scheme.
- The above description of the preferred embodiments has been given by way of example. From the disclosure given, those skilled in the art will not only understand the present invention and its attendant advantages, but will also find apparent various changes and modifications to the structures and methods disclosed. The applicant seeks, therefore, to cover all such changes and modifications as defined by the appended claims, and equivalents thereof.
Claims (15)
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP09290467.1A EP2264960B1 (en) | 2009-06-19 | 2009-06-19 | Method and processing arrangement for joint processing of uplink data |
EP09290467.1 | 2009-06-19 | ||
PCT/EP2010/055540 WO2010145873A1 (en) | 2009-06-19 | 2010-04-26 | Method and processing arrangement for joint processing of uplink data |
Related Parent Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/EP2010/055540 A-371-Of-International WO2010145873A1 (en) | 2009-06-19 | 2010-04-26 | Method and processing arrangement for joint processing of uplink data |
Related Child Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US14/737,838 Continuation US9276796B2 (en) | 2009-06-19 | 2015-06-12 | Method and processing arrangement for joint processing of uplink data |
Publications (1)
Publication Number | Publication Date |
---|---|
US20120163484A1 true US20120163484A1 (en) | 2012-06-28 |
Family
ID=41382135
Family Applications (2)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US13/379,179 Abandoned US20120163484A1 (en) | 2009-06-19 | 2010-04-26 | Method and processing arrangement for joint processing of uplink data |
US14/737,838 Active US9276796B2 (en) | 2009-06-19 | 2015-06-12 | Method and processing arrangement for joint processing of uplink data |
Family Applications After (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US14/737,838 Active US9276796B2 (en) | 2009-06-19 | 2015-06-12 | Method and processing arrangement for joint processing of uplink data |
Country Status (4)
Country | Link |
---|---|
US (2) | US20120163484A1 (en) |
EP (1) | EP2264960B1 (en) |
CN (1) | CN102439927B (en) |
WO (1) | WO2010145873A1 (en) |
Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20130265969A1 (en) * | 2011-11-25 | 2013-10-10 | Huawei Technologies Co., Ltd. | System, base station and method of signal processing |
US20150236827A1 (en) * | 2011-11-24 | 2015-08-20 | Huawei Technologies Co., Ltd. | Signal transmitting method and base station device |
US20150304867A1 (en) * | 2012-12-14 | 2015-10-22 | Telefonaktiebolaget L M Ericsson (Publ) | Backhaul Communication in Wireless Networks |
US20160150512A1 (en) * | 2013-08-09 | 2016-05-26 | Fujitsu Limited | Information Exchange Method, Base Station and Communication System |
US20160157255A1 (en) * | 2013-06-25 | 2016-06-02 | Huawei Technologies Co., Ltd. | Data scheduling method, apparatus, base station, and system |
US11641645B2 (en) * | 2017-03-01 | 2023-05-02 | Skyfive Ag | Device for a cellular communications network and method of operating such device |
US11963113B2 (en) * | 2019-08-09 | 2024-04-16 | Qualcomm Incorporated | Estimating a timing for a non-serving cell of a user equipment |
Families Citing this family (12)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US9100985B2 (en) * | 2011-02-15 | 2015-08-04 | Htc Corporation | Coordinated multi-point communications system and methods for controlling coordinated multi-point transmission and reception |
PL2493259T3 (en) * | 2011-02-21 | 2014-03-31 | Ntt Docomo Inc | Method for transmitting data between terminals of wireless communication system, node, and wireless communication system |
WO2013044517A1 (en) * | 2011-09-30 | 2013-04-04 | 富士通株式会社 | Uplink signal transmission method, user equipment and base station in coordinated multi-point system |
WO2013184051A1 (en) * | 2012-06-05 | 2013-12-12 | Telefonaktiebolaget L M Ericsson (Publ) | Method for selecting antennas to be included in a set of receiving antennas |
WO2015113499A1 (en) * | 2014-01-28 | 2015-08-06 | Mediatek Singapore Pte. Ltd. | Time domain multiplexing ul transmission on multiple serving cells for a mobile station with single transmitter |
US9907059B1 (en) * | 2016-05-27 | 2018-02-27 | Sprint Spectrum L.P. | Compensating delay spread in coordinated uplink communications |
US10164814B1 (en) | 2016-07-18 | 2018-12-25 | Sprint Spectrum L.P. | Offset decoding of resource elements within resource blocks to compensate for propagation delay |
US20180062801A1 (en) * | 2016-08-24 | 2018-03-01 | Qualcomm Incorporated | Techniques for wireless communications in coordinated multi-point operation |
US10117241B1 (en) | 2016-09-26 | 2018-10-30 | Sprint Spectrum L.P. | Transport block size adjustment to accommodate delay-based reduction of data volume in resource blocks |
US11057957B2 (en) * | 2018-10-09 | 2021-07-06 | Cable Television Laboratories, Inc. | Systems and methods for joint wireless transmission and joint wireless reception |
EP3772226B1 (en) * | 2019-07-30 | 2023-01-25 | Volkswagen AG | Methods, computer programs, and apparatuses for a command center and a vehicle |
WO2022066077A1 (en) * | 2020-09-25 | 2022-03-31 | Telefonaktiebolaget Lm Ericsson (Publ) | Scheduling uplink data in a multi-connectivity network |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5663958A (en) * | 1996-02-22 | 1997-09-02 | Telefonaktiebolaget Lm Ericsson | Method and apparatus for dynamically selecting the length of mobile station burst communications on the reverse digital control channel |
US6011787A (en) * | 1996-03-21 | 2000-01-04 | Ntt Mobile Communications Network Inc. | CDMA mobile communication scheme with effective use of sector configuration |
US20080239938A1 (en) * | 2006-03-30 | 2008-10-02 | Beceem Communications Inc. | Method and system for uplink coordinated reception in orthogonal frequency division multiple access systems |
US20110183669A1 (en) * | 2008-09-30 | 2011-07-28 | Muhammad Kazmi | Methods and Arrangments for Dynamically Adjusting the Rate of Sub Cell Searching in Coordinated Multiple Point Transmission/Reception, Comp, Cells |
Family Cites Families (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7058422B2 (en) * | 2000-09-20 | 2006-06-06 | Bae Systems Information And Electronic Systems Integration Inc. | Method for overusing frequencies to permit simultaneous transmission of signals from two or more users on the same frequency and time slot |
US6496535B2 (en) * | 2001-03-23 | 2002-12-17 | Navini Networks, Inc. | Method and system for effective channel estimation in a telecommunication system |
US7397864B2 (en) * | 2002-09-20 | 2008-07-08 | Nortel Networks Limited | Incremental redundancy with space-time codes |
US7453946B2 (en) * | 2003-09-03 | 2008-11-18 | Intel Corporation | Communication system and method for channel estimation and beamforming using a multi-element array antenna |
JP4974641B2 (en) | 2006-10-24 | 2012-07-11 | 三洋電機株式会社 | Wireless device |
-
2009
- 2009-06-19 EP EP09290467.1A patent/EP2264960B1/en not_active Not-in-force
-
2010
- 2010-04-26 US US13/379,179 patent/US20120163484A1/en not_active Abandoned
- 2010-04-26 CN CN201080022749.6A patent/CN102439927B/en not_active Expired - Fee Related
- 2010-04-26 WO PCT/EP2010/055540 patent/WO2010145873A1/en active Application Filing
-
2015
- 2015-06-12 US US14/737,838 patent/US9276796B2/en active Active
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5663958A (en) * | 1996-02-22 | 1997-09-02 | Telefonaktiebolaget Lm Ericsson | Method and apparatus for dynamically selecting the length of mobile station burst communications on the reverse digital control channel |
US6011787A (en) * | 1996-03-21 | 2000-01-04 | Ntt Mobile Communications Network Inc. | CDMA mobile communication scheme with effective use of sector configuration |
US20080239938A1 (en) * | 2006-03-30 | 2008-10-02 | Beceem Communications Inc. | Method and system for uplink coordinated reception in orthogonal frequency division multiple access systems |
US20110183669A1 (en) * | 2008-09-30 | 2011-07-28 | Muhammad Kazmi | Methods and Arrangments for Dynamically Adjusting the Rate of Sub Cell Searching in Coordinated Multiple Point Transmission/Reception, Comp, Cells |
Cited By (10)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20150236827A1 (en) * | 2011-11-24 | 2015-08-20 | Huawei Technologies Co., Ltd. | Signal transmitting method and base station device |
US9537627B2 (en) * | 2011-11-24 | 2017-01-03 | Huawei Technologies Co., Ltd. | Signal transmitting method and base station device |
US20130265969A1 (en) * | 2011-11-25 | 2013-10-10 | Huawei Technologies Co., Ltd. | System, base station and method of signal processing |
US9397730B2 (en) * | 2011-11-25 | 2016-07-19 | Huawei Technologies Co., Ltd. | System, base station and method of signal processing |
US20150304867A1 (en) * | 2012-12-14 | 2015-10-22 | Telefonaktiebolaget L M Ericsson (Publ) | Backhaul Communication in Wireless Networks |
US9883414B2 (en) * | 2012-12-14 | 2018-01-30 | Telefonaktiebolaget Lm Ericsson (Publ) | Backhaul communication in wireless networks |
US20160157255A1 (en) * | 2013-06-25 | 2016-06-02 | Huawei Technologies Co., Ltd. | Data scheduling method, apparatus, base station, and system |
US20160150512A1 (en) * | 2013-08-09 | 2016-05-26 | Fujitsu Limited | Information Exchange Method, Base Station and Communication System |
US11641645B2 (en) * | 2017-03-01 | 2023-05-02 | Skyfive Ag | Device for a cellular communications network and method of operating such device |
US11963113B2 (en) * | 2019-08-09 | 2024-04-16 | Qualcomm Incorporated | Estimating a timing for a non-serving cell of a user equipment |
Also Published As
Publication number | Publication date |
---|---|
CN102439927B (en) | 2014-10-01 |
EP2264960B1 (en) | 2014-10-01 |
EP2264960A1 (en) | 2010-12-22 |
US9276796B2 (en) | 2016-03-01 |
WO2010145873A1 (en) | 2010-12-23 |
US20150280955A1 (en) | 2015-10-01 |
CN102439927A (en) | 2012-05-02 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US9276796B2 (en) | Method and processing arrangement for joint processing of uplink data | |
JP4938037B2 (en) | OFDM transmitter and OFDM receiver | |
EP3267645B1 (en) | Methods and devices for time and frequency offset estimation | |
USRE43938E1 (en) | Device and method for compensating for phase distortion in base station of OFDMA-based cellular system | |
US8428001B2 (en) | Timing corrections in a multi carrier system and propagation to a channel estimation time filter | |
KR101002815B1 (en) | Interference noise estimation method, reception processing method, interference noise estimation apparatus, and receiver, in multicarrier communications system | |
EP2777337B1 (en) | Multi-stage timing and frequency synchronization | |
US8867570B2 (en) | Methods of transmitting pilot tones and data in spatial multiplexing transmission | |
WO2018202038A1 (en) | Uplink synchronization timing deviation determination method and device | |
EP2628254B1 (en) | Uplink noise estimation for virtual mimo | |
CN101945073A (en) | Pilot frequency-based time offset estimation device and method | |
US10644904B2 (en) | System and method for channel estimation | |
JPWO2007142313A1 (en) | Receiver and frequency information estimation method | |
CN104580057B (en) | A kind of time domain pilot and its synchronous method of single carrier MIMO system | |
KR20230091910A (en) | Reference signals in wireless communication systems | |
US9306788B2 (en) | SFO estimation technique for MIMO-OFDM frequency synchronization | |
CN102668483B (en) | Iq-imbalance estimation for non-symmetrical pilot symbols | |
JP5315676B2 (en) | MIMO communication apparatus and MIMO communication method | |
US7680027B2 (en) | Methods and systems for channel estimation in a collaborative multi input multiple output (MIMO) communication system | |
EP3334224B1 (en) | System of coordinating multi-cells and method thereof | |
US20150103932A1 (en) | Channel estimation method and receiver | |
EP2541798A1 (en) | Robust beamforming method and apparatus | |
US8213556B1 (en) | Signal power estimation for cellular OFDM systems | |
WO2009069088A2 (en) | Ici cancellation apparatus and method for ofdm systems | |
CN105282077A (en) | Uplink frequency offset correction method for LTE system |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
AS | Assignment |
Owner name: ALCATEL LUCENT, FRANCE Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:WILD, THORSTEN;DOETSCH, UWE;AYDIN, OSMAN;AND OTHERS;SIGNING DATES FROM 20100508 TO 20100525;REEL/FRAME:027852/0612 |
|
AS | Assignment |
Owner name: CREDIT SUISSE AG, NEW YORK Free format text: SECURITY AGREEMENT;ASSIGNOR:LUCENT, ALCATEL;REEL/FRAME:029821/0001 Effective date: 20130130 Owner name: CREDIT SUISSE AG, NEW YORK Free format text: SECURITY AGREEMENT;ASSIGNOR:ALCATEL LUCENT;REEL/FRAME:029821/0001 Effective date: 20130130 |
|
AS | Assignment |
Owner name: ALCATEL LUCENT, FRANCE Free format text: RELEASE BY SECURED PARTY;ASSIGNOR:CREDIT SUISSE AG;REEL/FRAME:033868/0555 Effective date: 20140819 |
|
STCB | Information on status: application discontinuation |
Free format text: ABANDONED -- FAILURE TO PAY ISSUE FEE |
|
AS | Assignment |
Owner name: OMEGA CREDIT OPPORTUNITIES MASTER FUND, LP, NEW YORK Free format text: SECURITY INTEREST;ASSIGNOR:WSOU INVESTMENTS, LLC;REEL/FRAME:043966/0574 Effective date: 20170822 Owner name: OMEGA CREDIT OPPORTUNITIES MASTER FUND, LP, NEW YO Free format text: SECURITY INTEREST;ASSIGNOR:WSOU INVESTMENTS, LLC;REEL/FRAME:043966/0574 Effective date: 20170822 |
|
AS | Assignment |
Owner name: WSOU INVESTMENTS, LLC, CALIFORNIA Free format text: RELEASE BY SECURED PARTY;ASSIGNOR:OCO OPPORTUNITIES MASTER FUND, L.P. (F/K/A OMEGA CREDIT OPPORTUNITIES MASTER FUND LP;REEL/FRAME:049246/0405 Effective date: 20190516 |