WO2015195004A1

WO2015195004A1 - Control apparatus and method of controlling the same

Info

Publication number: WO2015195004A1
Application number: PCT/SE2014/050745
Authority: WO
Inventors: Kannan SURESH KUMAR; Sailalith K; Abin JOSE; Reman KRISHNAN
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2014-06-17
Filing date: 2014-06-17
Publication date: 2015-12-23

Abstract

A control apparatus is operable to control allocation of a plurality of time slots in a TDMA-based wireless communication system. The apparatus receives a signal from a user equipment, calculates a value corresponding to a propagation delay of the signal, and determines whether the value calculated exceeds a first predetermined threshold. The apparatus converts two adjacent time slots from the plurality of time slots into a single extended time slot in response to it being determined that the value corresponding to the propagation delay exceeds the first predetermined threshold, and allocates the single extended time slot to the user equipment.

Description

DESCRIPTION

CONTROL APPARATUS AND METHOD OF CONTROLLING THE SAME

TECHNICAL FIELD

[0001] The present invention generally relates to a control apparatus, and a method of controlling the same .

BACKGROUND

[0002] In Time Division Multiple Access (TDMA) based communication systems, such as Global System for Mobile communications (GSM) systems, a wireless

resource is typically divided into a plurality of carriers which correspond to particular frequencies.

The carriers are further divided into frames, each of which comprises a number of sequential time slots.

Such time slots are allocated by a control apparatus such as a base station controller (BSC) to user

equipments (UE) to be used for communication.

[0003] A UE will periodically transmit signals to a base transceiver station (BTS), which serves a cell in which the UE is located, so that the signals are received by the BTS within the time slot allocated to the UE . In a typical case in which the TDMA frames are divided into eight time slots, eight separate UEs can share the same channel by timing their signals to arrive at the BTS in the corresponding eight time slots. [0004] Because the signals from the UE to the BST travel at the speed of light, which is finite, the distance between the UE and the BTS must be taken into account in order to time the signal transmissions so that they arrive at the BTS in the correct time slot. The delay in a transmitted signal arriving at the BTS from the UE due to the distance between the BTS and the UE is referred to as propagation delay. The BTS measures the propagation delay of a signal from the UE, and notifies the UE with a value corresponding to the propagation delay known as a timing advance (TA) .

Typically values of the TA transmitted to the UE range from 0 (for example, immediately beside the BTS) to 63. This is because the TA that is transmitted to the UE is typically coded by 6 bits. The UE can use the TA value to time its signal to arrive within the correct time slot by transmitting the signal in advance of the time slot in accordance with the TA value. Therefore, the TA values correspond to ranges of distances from the BTS, with larger TA values corresponding to larger distances from the BTS (for example, in GSM, each of the TAs from 1 to 63 correspond to concentric circular bands that are 550m wide and successively farther from the BTS) .

[0005] When the UE wishes to request for a

communication channel, in response to a synchronization signal transmitted from the BTS to the UE, and the UE transmits a signal known as an access burst to the BTS. An initial TA can be calculated based on how delayed the arrival at the BTS this access burst is. When this access burst is transmitted from the UE to the BTS, the UE does not yet have a TA value to indicate how far it is from the BTS. Therefore, it is necessary that the access burst include a guard band at the end of the transmission that is large enough to allow for the propagation delay of the signal. The size of this guard band effectively sets a maximum distance away from the cell that a UE can be. Typically this guard band comprises the last 68.27 bits out of a 156.25 bit access burst. In such a case, assuming a Gaussian Minimum Shift Keying (GMSK) modulation method in which a single bit is transmitted in approximately 3.69 με, this maximum distance can be approximated as follows: (68.27bit) * Ο.βθ β/ ί:) * Ρθθΐΐΐ/με) / (2) = 37.8km

Note that 300πι/μ3 is an approximation of the speed of light, and the division by 2 accounts for the round trip of the signals between the BTS and the UE . Thus, if the UE is more than roughly 37.8km from the BTS, the guard band will be insufficiently large, and the data portion of the access burst will arrive at the BTS within the subsequent time slot, potentially causing interference with another UE . Note that in GSM, the maximum distance of a cell is standardized at 35km rather than 37.8km. [0006] In some GSM implementations, an extended range function has been introduced to extend the radius of a cell beyond the maximum distance imposed on the system by the size of the guard band. With the

extended range function, the same TA values are used by the UE (typically 0 to 63), and these correspond to the same ranges of distances from the BTS as in the normal case. However, for every call, two adjacent

(consecutive) time slots are allocated instead of one. Whenever the UE is located beyond the maximum range in the normal case (35km, for example), it uses the

maximum TA value (typically 63), and its signal arrives at the BTS in the second of the two ad acent time slots. In the case of such an implementation, the range of a cell can typically be extended to roughly 120km. Here, the upper limit of the range is determined by the maximum TA value (63, for example) that can be sent to the UE rather than the size of the access burst guard band. For detailed information regarding extended range, please refer to 3GPP TS 45.010 vll.1.0, Radio Subsystem Synchronization.

[0007] Using two time slots for every user instead of one allows for a much larger cell range, but this also causes the capacity of the cell to be reduced.

There is a need for solutions that can extend the range of a cell in a TDMA-based wireless communication system while minimizing such a reduction in capacity. SUMMARY

[0008] The present invention was conceived in view of the above circumstances, and it is an object thereof to provide a technique of extending a range of a cell in a TDMA-based wireless communication system while minimizing a reduction of cell capacity.

[0009] According to a first aspect of the present invention, there is provided a control apparatus operable to control allocation of a plurality of time slots in a TDMA-based wireless communication system. The apparatus comprises a communication unit configured to receive a signal from a user equipment, a

calculation unit configured to calculate a value corresponding to a propagation delay of the signal received by the communication unit, and a determination unit configured to determine whether the value

calculated by the calculation unit exceeds a first predetermined threshold. The apparatus also comprises a conversion unit configured to convert two adjacent time slots from the plurality of time slots into a single extended time slot in response to the

determination unit determining that the value

corresponding to the propagation delay exceeds the first predetermined threshold, and an allocation unit configured to allocate the single extended time slot to the user equipment. [0010] According to a second aspect of the present invention, there is provided a method of controlling a control apparatus operable to control allocation of a plurality of time slots in a TDMA-based wireless

communication system. The method comprises a

communication step of receiving a signal from a user equipment, a calculation step of calculating a value corresponding to a propagation delay of the signal received in the communication step, and a determination step of determining whether the value calculated in the calculation step exceeds a first predetermined

threshold. The method also comprises a conversion step of converting two adjacent time slots from the

plurality of time slots into a single extended time slot in response to it being determined in the

determination step that the value corresponding to the propagation delay exceeds the first predetermined threshold, and an allocation step of allocating the single extended time slot to the user equipment.

[0011] By virtue of the above features, it is possible to extend a range of a cell in a TDMA-based wireless communication system while minimizing a

reduction of cell capacity.

[0012] Further features and advantages of the present invention will be apparent from the following description with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF DRAWINGS

[0013] Fig. 1 is an overall view for explaining a TDMA-based communication system according to some embodiments .

[0014] Fig. 2 is a functional block diagram of a control apparatus (BSC) according to some embodiments.

[0015] Fig. 3 is a flowchart for illustrating processing of the control apparatus (BSC) for

allocating time slots according to some embodiments.

[0016] Fig. 4 is a flowchart for illustrating processing of the BSC for allocating time slots according to some embodiments.

[0017] Fig. 5 is a flowchart for illustrating processing of the BSC for allocating time slots according to some embodiments.

[0018] Figs. 6A-6D are views for illustrating a reallocation of a call from a full-rate channel to a half-rate channel.

DETAILED DESCRIPTION

[0019] Fig. 1 is an overall view for explaining a

TDMA-based communication system according to some embodiments. In some embodiments the system is a GSM system.

[0020] In Fig. 1, a BTS 101 serves a cell in which a UE 103 is located. The BTS 101 is connected

communicably to a BSC 102. The BSC 102 is a control apparatus operable to control allocation of a plurality of time slots in the TDMA-based communication system. For example, when the UE 103 requests a channel over which to communicate, the BSC 102 controls allocation of one or more time slots to UE 103. It should be noted that in some embodiments there will be more UEs 103 in the cell. Also, in some embodiments there will be more cells, and each cell will have a corresponding BTS 101 and BSC 102. It should also be noted that while the control apparatus is explained as the BSC 102 in this example, in other embodiments the control apparatus may be implemented as a BTS, or as a

combination of a BSC and a BTS or another apparatus, for example.

[ 0021 ] The BSC 102, according to some embodiments, calculates a timing advance (TA) , which is a value corresponding to a propagation delay of a signal received from the UE 103. When the BSC 102 determines that the value of the TA exceeds a first predetermined threshold, the BSC 102 dynamically converts two

adjacent time slots from the plurality of time slots into a single extended time slot. The BSC 102 then allocates the extended time slot to the UE 103, which extends the range of the cell for the UE 103. In some embodiments, the single extended time slot provides a range of approximately 120km, while a normal time slot provides a range of approximately 35km. Note that while, in the example of Fig. 1, the BSC 102 is located outside of the extended range of the cell, in some embodiments the BSC 102 may be located close to the BTS 101.

[0022] The BSC 102 may dynamically convert two adjacent time slots into an extended time slot when the TA is initially calculated from the Random Access

CHannel (RACH) burst. In other cases, the BSC 102 may dynamically convert the two adjacent time slots into the extended time slot during an ongoing call when the UE 103 moved further away from the BTS 101 during the call and caused the calculated TA to exceed the first predetermined threshold.

[0023] Conversely, when the UE 103, during an ongoing call, moves closer to the BTS 101 such that the calculated TA is no longer exceeding the first

predetermined threshold, the BSC 102 may convert the extended time slot back into two normal time slots.

This has the effect of making one of the two time slots available for another user, and thus increasing the capacity of the cell.

[0024] In some embodiments, the predetermined threshold is chosen to be less than a maximum TA value (typically 63) . In some implementations, when the TA for a UE 103, during an ongoing call, is calculated to be a maximum TA value (for example, 63), and

subsequently the UE 103 moves further away from the BTS 101 to a distance outside of the range of even the maximum TA value (for example, > 35km), the call is automatically dropped. Therefore, it may be

advantageous to set the predetermined threshold to be less than the maximum TA value in such cases, so that the conversion to the extended range time slot is performed before such a situation can arise.

[0025] Note that the maximum TA value here is the maximum TA value that can be sent to the UE 103 and not the maximum TA value that can be calculated based on the propagation delay of a signal from the UE 103. The TA value calculated by the BSC 102 is commonly referred to as a virtual timing advance (VTA) in systems in which an extended range function is implemented. The VTA is a value corresponding to the actual propagation delay calculated based on a signal from the UE 103. In some embodiments, the VTA may have a maximum value of 219, for example, which is larger than the maximum TA (63, for example) that can be sent to the UE 103.

[0026] Fig. 2 is a functional block diagram of the control apparatus (the BSC 102) according to some embodiments. Again, the control apparatus is not limited to the BSC 102, and may be a combination of the BTS 101 and the BSC 102, for example.

[0027] The BSC 102 comprises a central processing unit (CPU) 201, a random access memory (RAM) 202, a read-only memory (ROM) 203, a communication unit 204, a determination unit 205, a conversion unit 206, a

calculation unit 207, an allocation unit 208, and a rearranging unit 209. Note that there may be multiple instances of a component. The components may be

connected by a bus, and capable of communication with each other thereupon.

[0028] The communication unit 204 may include wired links, such as an Ethernet cable for example. It may include wireless links, via transmitting/receiving antennas for example. It is capable of communication with external devices such as the BTS 101, the UE 103, or the like, over one or more networks.

[0029] In some embodiments, the functionality of the units 205 through 209 is implemented by the CPU 201 executing a software program stored in the ROM 203 using the RAM 202 as a work area. The RAM 202, may hold management information such as a database, for example, that keeps track of which time slots are allocated to which users, or which time slots

correspond to normal time slots, and which time slots correspond to extended time slots. In some embodiments, the units 204 through 209 are implemented using

dedicated hardware. In other embodiments, the units

204 through 209 are implemented using a combination of software and hardware. The detailed operation of the units 204 through 209 will be described with reference to Figs. 3-5.

[0030] Fig. 3 is a flowchart for illustrating processing of the BSC 102 for allocating time slots according to some embodiments.

[0031] In step S301, the communication unit 204 of the BSC 102 receives a signal from the UE 103, via the BTS 101, for example. This signal may correspond to a signal transmitted from the UE 103 in order to request a new call (an access burst (AB) in a random access channel (RACH) , or the like) , or a signal transmitted from the UE 103 in the process of an on-going call (a normal burst, or the like), for example.

[0032] Next, in step S302, the calculation unit 207 of the BSC 102 calculates a value corresponding to a propagation delay of the signal received in step S301. The BSC 102 may calculate this value by comparing a time at which the signal was received by the BTS 101 relative to a time that the signal would be expected to be received by the BTS 101 from the UE 103 in a case where the UE 103 was at zero distance from the BTS 101 under static channel conditions. The value calculated by the calculation unit 207 in step S302 corresponds to a timing advance value. More specifically this timing advance (TA) value is a VTA value which may exceed the maximum value of the TA and which corresponds to the real signal propagation delay. [0033] In step S303, the determination unit 205 of the BSC 102 determines whether the value calculated by the calculation unit 207 in step S302 exceeds the first predetermined threshold. As mentioned early, this threshold may be chosen to be less than the maximum TA that is sent to the UE 103. In some embodiments, the maximum TA (MAXTA) is 63, and the first predetermined threshold is set to be 62 (MAXTA-1), for example.

[0034] When the determination unit 205 determines, in step S303, that the TA value calculated in step S302 exceeds the first predetermined threshold, the

processing proceeds to step S304, and the conversion unit 206 of the BSC 102 converts two adjacent time slots from the plurality of the time slots into a single extended time slot. Specifically, the

conversion unit 206 updates management information stored in a storage medium such as the RAM 202 so that the management information indicates that the two adjacent time slots correspond to the single extended time slot rather than two individual normal time slots. Note that the conversion unit 206 may perform this conversion in response to the determination unit 205 determining that the two adjacent time slots are available for allocation.

[0035] Next, in step S305, the allocation unit 208 of the BSC 102 allocates the extended time slot to the UE 103. For example, the BSC 102 may update management information stored in a storage medium such as the RAM 202 to indicate that the extended time slot is

allocated to the UE 103. The BSC 102 may notify the UE 103 of the allocation by transmitting an assignment message to the UE 103, indicating information about the time slot.

[0036] When the determination unit 205 determines, in step S303, that the TA value calculated in step S302 does not exceed the first predetermined threshold, normal operation is performed in step S306.

Specifically, in step S306, the BSC 102 allocates a normal time slot to the UE 103, if one is available for allocation .

[0037] By converting two adjacent time slots into an extended time slot when the TA is calculated to exceed a threshold, as in the processing explained with reference to Fig. 3, it is possible to extend a range of a cell in a TDMA-based wireless communication system while minimizing a reduction of cell capacity. This is because two time slots (an extended time slot) are only used for calls of UEs 103 that require an extended time slot. In other words, extended time slots are not designated unnecessarily, and so the number of

available time slots is maximized. Furthermore, by choosing the threshold to be less than the maximum TA that is sent to the UE 103, a situation in which the call is dropped due to the UE 103 moving beyond the range corresponding to this maximum TA can be avoided.

[0038] Fig. 4 is a flowchart for illustrating processing of the BSC 102 for allocating time slots according to some embodiments. Steps that are the same as in Fig. 3 are labeled with the same reference

characters. By the processing according to Fig. 4, it is possible to guarantee that a minimum number of extended range calls, and a minimum number of normal calls can be made at any given time.

[0039] The processing of Fig. 4 continues from step S302, described above with reference to Fig. 3. In embodiments illustrated by Fig. 4, a predetermined number of reserved extended time slots are fixed in advance. In other words, these extended time slots are pre-designated as extended range time slots, and they are only used as extended time slots. This makes it possible to guarantee that a minimum number of extended range calls can be performed at any given time.

[0040] When, in step S303, the determination unit 205 determines that the TA (VTA) does not exceed the predetermined threshold (MAXTA-1), the processing proceeds to step S306 and normal operation is performed, as in Fig. 3. On the other hand, when, in step S303, the determination unit 205 determines that the TA (VTA) exceeds the predetermined threshold (MAXTA-1), the processing proceeds to step S401, and the determination unit 205 determines whether any of the predetermined number of reserved extended time slots are available for allocation. When the determination unit 205 determines that one of these extended time slots is available for allocation, the processing proceeds to step S402, and the allocation unit 208 allocates the available extended time slot to the UE 103.

[0041] On the other hand, when the determination unit 205 determines, in step S401, that none of the predetermined number of reserved extended time slots are available for allocation, the determination unit 205 determines, in step S403, whether the number of extended time slots that are currently allocated reaches a second predetermined threshold. This second predetermined threshold makes it possible to guarantee that a minimum number of normal range calls can be performed at any given time.

[0042] When the determination unit 205 determines that the number of extended time slots that are currently allocated reaches the second predetermined threshold, the call is blocked in step S404.

[0043] On the other hand, when the determination unit 205 determines, in step S403, that the number of extended time slots that are currently allocated does not reach the second predetermined threshold, the processing proceeds to step S304, and the conversion unit 206 converts two adjacent time slots into an extended time slot. Note that here the conversion unit 206 converts the two adjacent time slots in response to the determination unit 205 determining that the number of extended time slots that are currently allocated does not reach the second predetermined threshold.

Note also, the conversion unit 206 converts the two adjacent time slots in response to the determination unit 205 determining that none of the predetermined number of reserved extended time slots are available for allocation. Next in step S305, the allocation unit allocates the extended time slot to the UE 103, as in Fig. 3.

[0044] By maintaining a predetermined number of reserved extended time slots that are fixed in advance, and by using the second predetermined threshold, the processing according to Fig. 4 enables a minimum number of extended calls and a minimum number of normal calls to be guaranteed to be possible in combination with extending the range of the cell dynamically to minimize capacity loss. Note that in some embodiments the reserved extended timeslots are maintained but the second predetermined threshold is not employed, and that in other embodiments, the second predetermined threshold is employed, but the reserved extended timeslots are not maintained.

[0045] Fig. 5 is a flowchart for illustrating processing of the BSC 102 for allocating time slots according to some embodiments. Steps that are the same as in Fig. 3 or Fig. 4 are labeled with the same

reference characters. By the processing according to Fig. 5, it is possible for the rearranging unit 209 to rearrange (shift) ongoing calls in order to make space for an extended range call.

[0046] The processing of Fig. 5 continues from step S302, as described above with reference to Fig. 3. When, in step S303, the determination unit 205

determines that the TA (VTA) does not exceed the

predetermined threshold (MAXTA-1), the processing proceeds to step S306 and normal operation is performed, as in Fig. 3. On the other hand, when, in step S303, the determination unit 205 determines that the TA (VTA) exceeds the predetermined threshold (MAXTA-1), the determination unit 205 determines, in step S501,

whether two adjacent time slots are available for allocation .

[0047] When, in step S501, the determination unit

205 determines that two adjacent time slots are

available, the processing proceeds to step S304 and then to step S305, and the two adjacent time slots are converted into an extended time slot, and the extended time slot is allocated to the UE 103 respectively, as in Fig. 3.

[0048] However, when the determination unit 205 determines that two adjacent time slots are not

currently available, the determination unit 205, in step S502, determines whether or not there exist any two time slots that are currently available. When the determination unit 205 determines, in step S502, that there are two time slots that are currently available, the processing proceeds to step S503, and the

rearranging unit 209 shifts a call (an ongoing call of a UE other than the UE 103) for which a timeslot, which is adjacent to one of the available time slots, is used to a different time slot (different from the time slot that was used for the call up until then) . After this shifting there are two adjacent available time slots.

[0049] For example, Fig. 6A is a view showing an example of allocation of time slots prior to step S502. Time slots tO, tl, t2, t4, t5 and t6 are allocated to users A, B, C, D, E and F, respectively, and FR channel calls are ongoing in these time slots. Time slots t3 and t7 are available for allocation, but because t3 and tl are not adjacent to each other, they cannot be converted into a single extended time slot.

[0050] In other words, in step S501, the

determination unit 205 determines that two adjacent time slots are not currently available. However, in step S502, the determination unit 205 determines that there are two time slots that are currently available since time slot t3 and time slot t7 are available.

[0051] Then, in step S503, the rearranging unit

209 shifts the call of User C from time slot t2 to time slot t7. In some embodiments, the rearranging unit 209 shifts the call by performing an intra-cell handover, for example. In this example the rearranging unit 209 chooses to shift the call of user C from time slot t2 to time slot t7 rather than the call of user D, or the call of user F.

[0052] The choice of which call to shift may be performed based on a value indicating the quality of a call, for example. The value indicating the quality of the call may be a value reported from the UE 103 in a measurement report (RXQUAL, for example), for example. The value indicating the quality of the call is not limited to measurement reports, however, and may be any value that indicates the quality of the call. The value indicating the quality of the call may be stored in a storage medium, such as the RAM 202, for example. In some embodiments, the rearranging unit 209 chooses a call having a lower quality than other candidates in order to improve a carrier-to-interference ratio of the call by the shifting.

[0053] Fig. 6B is a view for showing an example of the allocations of the time slots of Fig. 6A after the shifting of step S503. Because of the shifting, time slots t2 and t3, which are adjacent, became available for allocation. This means that time slots t2 and t3 can be converted by the conversion unit 206 into a single extended range time slot in step S304. [0054] Returning to Fig. 5, after the rearranging unit 209 shifts the call in step S503, the processing proceeds to step S304 and then to step S305, and the two adjacent time slots are converted into an extended time slot, and the extended time slot is allocated to the UE 103 respectively, as in Fig. 3.

[0055] Meanwhile, when the determination unit 205 determines, in step S502, that there are not two time slots that are currently available, the processing proceeds to step S504. In step S504, the determination unit 205 determines whether or not there exists an ongoing call (a call of a UE other than the UE 103) that uses a full-rate (FR) channel. If such an ongoing call exists, the determination unit 205 also determines whether a value indicating a quality of the call exceeds a third predetermined threshold. The value indicating the quality of the call may be a value reported from the UE 103 in a measurement report

(RXQUAL, for example), for example. The value

indicating the quality of the call is not limited to measurement reports, however, and may be any value that indicates the quality of the call. The value

indicating the quality of the call may be stored in a storage medium, such as the RAM 202, for example. The third predetermined threshold may be chosen as a minimum quality value for which shifting of the call from full-rate (FR) to half-rate (HR) can be performed while maintaining a sufficient level of quality of the call .

[0056] When, in step S504, the determination unit

205 determines that there exists no ongoing call using an FR channel whose quality is indicated by the value to exceed the third predetermined threshold, the processing proceeds to step S404, and the call is blocked, as in Fig. 4. However, when the determination unit 205 determines, in step S504, that there does exist an ongoing call using an FR channel whose quality is indicated by the value to exceed the third

predetermined threshold, the processing proceeds to step S505. In step S505, the rearranging unit 209 shifts the call from FR to HR. In some embodiments, the rearranging unit 209 shifts the call from FR to HR, but the time slot of the call remains the same. In some embodiments this is a reallocation to another time slot .

[0057] For example, Fig. 6C is a view showing an example of allocation of time slots prior to step S504. In the situation shown in Fig. 6C, time slots tO, t2, t4, t5, t6 and t7 are allocated to users A, C, D, E, F and G respectively, and FR channel calls are ongoing in these time slots. Also, time slot tl is allocated to user B, and an HR channel call is ongoing in this time slot. Time slot t3 is currently available for

allocation . [0058] In step S502, the determination unit 205 determines that there are no two time slots that are currently available, because only time slot t3 is available for allocation. In step S504, the

determination unit 205 determines that the call of user C in time slot t2 is a FR call, and that the quality of this call exceeds the third predetermined threshold. So, the rearranging unit 209 shifts the FR call of user C in time slot t2 to a HR call in time slot tl in step S505.

[0059] Fig. 6D shows an example of the allocations of the time slots for the calls of Fig. 6C after the shifting (reallocation) of step S504. By the shifting in step S505, time slot t2, which is adjacent to the available time slot t3, becomes available. Thus, due to the shifting in step S505, time slots t2 and t3 can be converted into an extended time slot by the

conversion unit 206. In other words, by the

rearranging unit 209 shifting the call from FR to HR, one of the two adjacent time slots (time slot t2) is caused to become available for the conversion by the conversion unit 206. In some embodiments, the

allocation unit 208 shifts the call from FR to HR by performing an intra-cell handover, for example. After step S505, the processing returns to step S501, and the determination unit 205 determines that two adjacent time slots are available. The processing then proceeds to step S304 and then to step S305, and the two

adjacent time slots are converted into an extended time slot, and the extended time slot is allocated to the UE 103 respectively, as in Fig. 3.

[0060] In some embodiments, the rearranging unit

209, in step S505, preferentially shifts a call that does not use an extended time slot (a normal call) over another call that does use an extended time slot (an extended range call) . This may be advantageous because a normal call may be more likely to be able to continue at the minimum level of quality after conversion to HR than an extended range call. In such cases, the determination of step S504 may be performed first for normal calls, and then for extended calls only when it is determined that there are no normal calls that satisfy the determination.

[0061] In some embodiments, the shifting

processing explained in Fig. 5 is performed

independently of a call setup process. For example, the processing corresponding to step S501-step S505 may be performed on the BSC 102 independently from the BSC 102 receiving the signal from the UE 103 in step S301 for setting up a call. In such a case, the shifting processing may be triggered by a condition such as a predetermined percentage of the reserved extended time slots being allocated, for example. Performing this processing independently may be advantageous in that doing so avoids slowing down the call setup process, for example, while still causing adjacent time slots to become available for allocation.

[0062] By shifting ongoing calls, as in the processing explained with reference to Fig. 5, it is possible to cause adjacent time slots, which can be converted into extended time slots, to become available for allocation. This can increase capacity, increase call quality, and reduce the number of dropped calls in the cell. Note that the embodiments described with reference to Fig. 4 may be combined with the

embodiments explained with reference to Fig. 5.

[0063] By virtue of the processing explained above, it is possible to extend a range of a cell in a TDMA- based wireless communication system while minimizing a reduction of cell capacity.

[0064] The present invention is not limited to the above-described embodiments, and various changes and modifications can be made within the spirit and scope of the present invention. Therefore, to apprise the public of the scope of the present invention, the following claims are made.

Claims

1. A control apparatus (102) operable to control allocation of a plurality of time slots in a TDMA-based wireless communication system, the apparatus

comprising:

a communication unit (204) configured to receive a signal from a user equipment (103);

a calculation unit (207) configured to calculate a value corresponding to a propagation delay of the signal received by the communication unit;

a determination unit (205) configured to

determine whether the value calculated by the

calculation unit exceeds a first predetermined

threshold;

a conversion unit (206) configured to convert two adjacent time slots from the plurality of time slots into a single extended time slot in response to the determination unit determining that the value

corresponding to the propagation delay exceeds the first predetermined threshold, and

an allocation unit (208) configured to allocate the single extended time slot to the user equipment.

2. The control apparatus according to claim 1, wherein

the determination unit determines whether the two adjacent time slots are available for allocation, and the conversion unit converts the two adjacent time slots into the single extended time slot in response to the determination unit determining that the two adjacent time slots are available for allocation.

3. The control apparatus according to claim 1 or 2, wherein

the determination unit determines whether any of a predetermined number of reserved extended time slots are available for allocation, and

the conversion unit converts the two adjacent time slots in response to the determination unit determining that none of the reserved extended time slots are available for allocation.

4. The control apparatus according to any one of claims 1-3, wherein

the determination unit determines whether a number of extended time slots that are currently allocated reaches a second predetermined threshold, and the conversion unit converts the two adjacent time slots in response to the determination unit determining that the number of extended time slots that are currently allocated does not reach the second predetermined threshold.

The control apparatus according to any one claims 1-4, further comprising

a rearranging unit (209) configured to shift a call to a different time slot, wherein

one of the two adjacent time slots is caused to become available for the conversion by the conversion unit by the rearranging unit shifting the call to the different time slot.

6. The control apparatus according to claim 5, wherein

the determination unit further determines whether there are two adjacent time slots that are both available, and

the rearranging unit shifts the call to the different time slot in response to the determination unit determining that there are not two adjacent time slots that are both available.

7. The control apparatus according to claim 5 or 6, wherein

the rearranging unit shifts the call to the different time slot independently of a call setup process .

8. The control apparatus according to any one of claims 5-7, wherein

the rearranging unit shifts the call to the different time slot by performing an intra-cell handover .

9. The control apparatus according to any one of claims 5-8, wherein

the determination unit determines whether or not there are two time spots that are available, and

the rearranging unit shifts the call from full- rate to half-rate in response to the determination unit determining that there are not two time slots that are available .

10. The control apparatus according to claim 9, wherein

the rearranging unit, because the call is not an extended range call, shifts the call from full-rate to half-rate preferentially over another call that is an extended range call.

11. The control apparatus according to any one of claims 1-10, wherein

the value calculated by the calculation unit corresponds to a timing advance value, and the first predetermined threshold is less than a maximum timing advance value.

12. A method of controlling a control apparatus (102) operable to control allocation of a plurality of time slots in a TDMA-based wireless communication system, the method comprising:

a communication step (S301) of receiving a signal from a user equipment (103);

a calculation step (S302) of calculating a value corresponding to a propagation delay of the signal received in the communication step;

a determination step (S303) of determining whether the value calculated in the calculation step exceeds a first predetermined threshold;

a conversion step (S304) of converting two adjacent time slots from the plurality of time slots into a single extended time slot in response to it being determined in the determination step that the value corresponding to the propagation delay exceeds the first predetermined threshold, and

an allocation step (S305) of allocating the single extended time slot to the user equipment.

13. The method according to claim 12, wherein

it is determined whether the two adjacent time slots are available for allocation, and

the two adjacent time slots are converted, in the conversion step, into the single extended time slot in response to it being determined that the two adjacent time slots are available for allocation.

14. The method according to claim 12 or 13, wherein it is determined whether any of a predetermined number of reserved extended time slots are available for allocation, and

the two adjacent time slots are converted, in the conversion step, in response to it being determined that none of the reserved extended time slots are available for allocation.

15. The method according to any one of claims 12-14, wherein

it is determined whether a number of extended time slots that are currently allocated reaches a second predetermined threshold, and

the two adjacent time slots are converted, in the conversion step, in response to it being determined that the number of extended time slots that are currently allocated does not reach the second

predetermined threshold.

16. The method according to any one of claims 12-15, further comprising

a rearranging step of shifting a call to a different time slot, wherein

one of the two adjacent time slots is caused to become available for the conversion in the conversion step by the call being shifted, in the rearranging step, to the different time slot.

17. The method according to claim 16, wherein

it is determined whether there are two adjacent time slots that are both available, and

the call is shifted, in the rearranging step, to the different time slot in response to it being

determined that there are not two adjacent time slots that are both available.

18. The method according to claim 16 or 17, wherein the call is shifted, in the rearranging step, to the different time slot independently of a call setup process.

19. The method according to any one of claims 16-18, wherein

the call is shifted, in the rearranging step, to the different time slot by performing an intra-cell handover .

20. The method according to any one of claims 16-19, wherein

it is determined whether or not there are two time spots that are available, and

the call is shifted, in the rearranging step, from full-rate to half-rate in response to it being determined that there are not two time slots that are available .

21. The method according to claim 20, wherein

in the rearranging step, because the call is not an extended range call, the call is shifted from full- rate to half-rate preferentially over another call that is an extended range call.

22. The method according to any one of claims 12-21, wherein

the value calculated in the calculation step

corresponds to a timing advance value, and the first predetermined threshold is less than a maximum timing advance value.