WO2002082705A1

WO2002082705A1 - A tdd framing method for a wireless system

Info

Publication number: WO2002082705A1
Application number: PCT/CN2001/001175
Authority: WO
Inventors: Li Daoben; Shui Ming Joseph Ho
Original assignee: Linkair Communications, Inc.
Priority date: 2001-04-09
Filing date: 2001-07-16
Publication date: 2002-10-17
Also published as: CN1193527C; CN1436410A

Abstract

A LAS-TDD framing method for physical layer of a wireless system, in which a LAS-TDD frame comprises a downlink sync SF, an uplink sync SF and traffic SFs, the method comprising the steps of calculating the number of chips per LAS-TDD frame based on chip rates and frame length; determining the number of chips for traffic SF by subtracting the number of chips for downlink sync SF and uplink sync SF from the number of chips per LAS-TDD frame; and determining the number of traffic SFs in the LAS-TDD frame and the number of chips in each traffic SF based on the length of the LA code. With the framing method according to the present invention, a large cell coverage can be achieved without any overlapping of the transmit and receive SFs.

Description

A TDD framing method for a wireless system

FIELD OF THE INVENTION

The invention relates generally to wireless communication methods,

and more specifically, to a framing method used in Time Division Duplex

(TDD), which can provide higher capacity and performance for mobile

communication services.

BACKGROUND OF THE INVENTION

Today, mobile communications are becoming one of the important

factors that influence our life. It is foreseen that the future

communications network will be the " mobile IP " network.

For " mobile ", the key is to support higher spectral efficiency

and higher moving speed. For " IP ", the key is to support asymmetric

traffic, higher throughput and smaller delay.

It is well known that the multiple access technology and the duplex

technology are the key technologies for system design. From the

technical viewpoint, the composite multiple access . scheme

FDMA/CDMA/TDMA with TDD can be capable of supporting the " mobile IP

" services.

The most important aspect of a wireless technology and system is

the availability of increased spectral efficiency. Most of the current

Third Generation Systems are restricted in their capacity and performance by limited spectral efficiency. In particularly, CDMA

systems (e. g. WCDMA, cdma2000 and TD-SCDMA) are limited by the inherent

system interference resulting from the use of the classic Walsh codes.

In addition to limiting the wireless system's spectral efficiency,

those codes make it challenging to design a large area TDD system. This

in turn makes it impossible to leverage the benefits of a TDD system

in a cellular network.

WO 99/09692, filed by Li Daoben, discloses a spread spectrum

multiple access coding method, in which a coding scheme called Large

Area code (LA code) is described. Figure 1 shows a LA code with 16 pulses

and length of 2387 chips. The spread spectrum access code consists of

basic pulses that have normalized amplitude, duration and polarity,

the number of basic pulses is ascertained by such practical factors:

the requested number of users, the number of usable pulse compression

codes, the number of usable orthogonal carrier frequencies, system

bandwidth and system maximal information rate, the intervals between

these basic pulses on time axis are various, and coding just utilizes

the dissimilarity of pulse positions and orders of pulses' polarities.

Large Area Synchronized Time Division Duplex (LAS-TDD) uses a new

spread-spectrum technology called LAS-CDMA (Large Area Synchronized

Code Division Multiple Access). LAS-CDMA is characterized by the use

of a newly spreading and encoding scheme based on LA and LS codes (LAS

coding) that reduce system-generated interference, thus increasing spectral efficiency and capacity.

LA codes are defined as a varying time interval pulse series. The

LA codes are used in an LAS-CDMA system to distinguish between different

cells and sectors. Different permutations of the primary LA code are

used in different cells and sectors of the cellular network.

Table 1 shows a primary LA code with 17 pulses with its corresponding

sequence of 17 time slots with different lengths.

Table 1 Primary LA-CDMA code

Considering a LA code with N pulses, as the order of N basic intervals

has no affect on its auto-correlation and cross-correlation functions,

it can be arbitrary. When a code group with various orders of basic

intervals is exploited at the same time, the number of users will

increase enormously.

The orthogonal characteristic or quasi-orthogonality of the LA

codes can serve as a solution for reducing interference of adjacent

service areas or channels.

The LA codes provide the random function necessary for multi-cell operation and at the same time contribute to the reduction in

interference between different cells and sectors.

Another benefit of the LA codes is that they allow the use of

complementary orthogonal codes such as the LS codes as described in

the following section (whereas scrambling methods would introduce

interference between complementary components of these codes).

PCT/CNOO/00028, filed by Li, Daoben with the title of "A Scheme

for Spread Spectrum Multiple Address Coding with Interference Free

Window", discloses complementary orthogonal codes referred to here

as LS codes. The LS codes have a "Interference Free Window (IFW)"

property, which is also referred to as "zero correlation window"

property. For example, consider the following four LS codes of length

8:

(Cl, SI) = (++-+, + )

(C2, S2) = (+++-, +-++)

(C3, S3) = (-+++, -+-)

(C4, S4) = (-+—, +)

The cross-correlation of any two of these codes is zero when the

time shift between the two codes is within the (inclusive) window [-1,

+1], and the auto-correlation of any of these codes is zero except when

there is no time shift. Thus these four codes have a IFW of [-1, +1].

Similarly, the following LS codes of length 16 have an Interference

Free Window of [-3, +3] : (Cl, SI) = (++-++++-, + +-++)

(C2, S2) = (++-+ +, + +—)

(C3, S3) = (+++-++-+, +-+++ )

(C4, S4) = (+++ +-, +-++-+++)

If we only consider (Cl, Si) and (C2, S2), they have a Interference

Free Window of [-7, +7].

Thus, when mobile stations transmit to a base station signals that

are modulated using a set of LS codes that have a Interference Free

Window of [-n, +n], these signals will not interfere with each other

as long as they arrive at the receiving base station within n chips

with respect to each other. This eliminates inter-symbol interferences

and multiple access interferences when multipath signals from a same

remote unit and signals from different mobile stationsarrive within

an Interference Free Window,

LS codes are defined as a family of variable length complementary

orthogonal codes. These codes are defined by two components - the C

section and the S section - each of which are defined recursively

according to a tree structure.

Besides their orthogonality, the main property of these codes is

the existence of an IFW. The IFW is an area of zero-correlation in

the non-cyclic cross-correlation of these codes taken two at a time.

In addition, the auto-correlation function of each LS code has no

sidelobes within the IFW. The length of the IFW varies according to the pair of LS codes chosen within the tree.

A consequence of the existence of the IFW is that the interference

resulting from a time-delayed collision between two transmitted

symbols, spreaded by different LS codes, will be cancelled, as long

as the value of the delay does not exceed the length of the IFW. Multiple

Access Interference (MAI) is therefore virtually cancelled on the

downlink as long as the channel's delay spread is less than the minimum

value of the IFW for the LS code-set considered. Generally, since most

of the received energy from other mobile station is concentrated within

a few chips delay (e. g. more than 90% of the received energy corresponds

to less than 5ms (i. e. less than 7 chips when the chip rate is 1.28

Mcps)), the downlink MAI in a LAS-CDMA system is reduced drastically.

On the uplink, the use of uplink synchronization ensures that all

uplink signals are received within the same IFW, which means that MAI

is also reduced in similar proportions..

The auto-correlation properties of the LS codes also ensure that

self-interference (the interference between delayed version of the

same channel, or Inter-Symbol Interference - ISI) is reduced to a

minimum on both the uplink and the downlink.

By reducing the same-sector interference to a minimum, the LS codes

provide the fundamental basis for an efficient wireless system.

The LAS-TDD is a multiple access system with a combination of time

division and code division multiple access schemes. A physical channel shall be described in two dimensions: time domain and code domain.

Different physical channels are separated in either time domain or code

domain.

In general, the behavior of traffic varies from location to location

and from time to time. In locations where voice is the predominant

traffic type, the traffic is more symmetrical and a frame structure

with 1:1 downlink-to-uplink radio is suitable for support traffic in

this location. On the other hand, in locations where web bowering is

the predominant traffic type, the traffic is very asymmetrical and a

frame structure with 3:1 or 4:1 downlink-to-uplink radio is suitable

for support traffic in this location. Furthermore, the traffic behavior

may change from time to time. In some locations, voice is the primary

traffic type during the business hour and Internet may be the primary

traffic type during the off peak hours. Thus, a method that allows the

dynamic re-configuration of LAS-TDD frame based on traffic statistics

collected at the coverage area at different times of the day is very

useful in enhancing the efficiency and the capacity of the cells.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a LAS-TDD framing

method for physical layer of a wireless system, which uses both spread

spectrum modulation and orthogonal codes that have a zero-correlation

window to provide a high capacity and high performance communications. Another object of the present invention is to provide a LAS-TDD

framing method that could reduce the Adjacent Cell Interference (ACI)

among signals from neighboring base stations and the mobile stations

that they serve.

The objects and advantages are achieved by the following method in

accordance with the present invention.

A LAS-TDD framing method for physical layer of a wireless system,

in which a LAS-TDD frame comprises a downlink sync SF, an uplink sync

SF and traffic SFs, the method comprising the steps of:

calculating the number of chips per LAS-TDD frame based on chip

rates and frame length;

determining the number of chips for traffic SF by subtracting the

number of chips for downlink sync SF and uplink sync SF from the number

of chips per LAS-TDD frame;

characterized in that

determining the number of traffic SFs in the LAS-TDD frame and the

number of chips in each traffic SF based on the length of the LA code.

An advantage of the present invention is that the LAS-TDD frame can

support alternating transmit and receive SF. At the same time, since

each of the SF in each frame can be allocated to either uplink or

downlink, it can ideally support asymmetric traffic, higher throughput

and smaller delay, in other words, the " mobile IP " services. That

is it allows LAS-TDD system to support different frame arrangements dynamically depending on the system requirements.

BRIEF DESCRIPTIONS OF THE DRAWINGS

The accompanying drawings which are incorporated in and constitute

a part of this specification, illustrate particular embodiments of the

invention, and together with the description, serve to explain, and

not restrict, the principles and advantages of the present invention.

Figure 1 shows a LA code with 16 pulses;

Figure 2 shows a frame structure of UTRA TDD defined in 3GPP

specifications;

Figure 3 shows a frame structure of TD-SCDMA defined in 3GPP

specifications;

Figure 4 shows the arrangement of the LS code within each time slot

of the LA code;

Figure 5 shows a LAS-TDD frame with distance gap and transition gap;

Figure 6 shows a LAS-TDD frame with the downlink traffic to uplink

traffic ratio of 1:1;

Figure 7 shows another LAS-TDD frame with the downlink traffic to

uplink traffic ratio of 1:1;

Figure 8 shows the relative position of the transmit and receive SFs

at different distances from the base station for downlink to uplink

traffic ratio of 1:1;

Figure 9 shows a LAS-TDD frame with a downlink traffic to uplink traffic ratio of 2:1;

Figure 10 shows the relative position of the transmit and receive

SFs at different distance from the base station for downlink to uplink

traffic ratio of 2:1;

Figure 11 shows the transmission structure for the downlink sync

channel and uplink sync channel;

Figure 12 shows a frame for the downlink sync channel;

Figure 13 shows a frame for the uplink sync channel;

Figure 14 shows an example of the traffic subframe;

Figure 15 shows an example of LS Subsections of 64 chips;

Figure 16 shows a traffic subframe type 1;

Figure 17 shows the transmission of control blocks in a subframe of

type 1;

Figure 18 shows a TFCI information is to be transmitted; and

Figure 19 shows a traffic subframe type 2.

DETAILED DESCRIPTIONS OF THE INVENTION

As we have known, a cellular wireless system normally comprises

multiple cells that serve a geographic area, a base station in each

cell providing a downlink signal to mobile stations in the cell, and

a plurality of mobile stations in each cell. In such a cell, base

station includes transmitters and receivers and appropriate processors.

Each of mobile stations also includes a transmitter, a receiver , and an appropriate processor.

Fig.2 shows a frame structure of UTRA TDD defined in 3GPP

specifications. Fig.3 shows a frame structure of TD-SCDMA defined in

3GPP specifications. While the TDD frame according to the present

invention can be designed to be compatible with UTRA TDD with chip rate

1.28 Mcps, which will have the similar frame structures with multiple

switching points.

For CDMA TDD system design, the frame structure is one of the key

factors. Some of the main concerns are capacity, coverage, flexibility,

and compatibility, which will be separately interpreted herewith.

The capacity is constrained by the interferences. The consequence

of these interference sources is a negative impact on system

performance and capacity. Many methods have been tried and used to

reduce these interferences. For example, in UTRA TDD and TD-SCDMA,

Joint Detection is used to reduce ISI and MAI, and smart antenna is

also used in TD-SCDMA to reduce interferences. Although these

technologies can improve the system performance with the expense of

system complexity, the biggest problem is that all the above

interferences cannot be eliminated to the ideal level due to the

drawbacks of system design.

In CDMA TDD system, the coverage is mainly determined by the gap

length between transmission and reception. The larger the switching

gap is, the larger the coverage will be supported. However, the gap length is contradicted with the capacity or spectral efficiency. In

UTRA TDD, the gap is so small that it is suitable for Pico-cell or

micro-cell environment. In TD-SCDMA, the gap is large enough to support

macro-cell environment, but it cannot efficiently support the smaller

cell because the fixed gap length.

Concerning flexibility, it is highly required that flexible

services can be supported in the TDD system in order to be capable for

"mobile IP" applications. One common way used in TDD system is dynamic

channel allocation. However, in UTRA TDD like CDMA TDD system, it is

not so efficient because there will be additional interferences

introduced into the system, and Joint Detection cannot work very well.

Concerning mobility, in the traditional CDMA TDD system, the fast

close-loop power control cannot be achieved because the power control

rate is determined by the frame length. The imperfect power control

will result severe degradation for system performance. And higher speed

mobility means fast channel fading, which is expected to be compensated

with fast power control. Thus, it cannot support high-speed mobility.

This is the case in UTRA TDD. In TD-SCDMA, another limitation for high

speed mobility is because of smart antenna.

The selected orthogonal spread spectrum codes can be LS codes. And

such a framing method, frame, or system that combines LA code and LS

code in TDD mode will be referred to as LAS-TDD mode hereinafter.

In the LAS-TDD mode, ISI and MAI can be reduced to zero, while ACI can be reduced to a marginal level. As long as multi-path signals from

same remote unit and signals from multiple mobile stations are

synchronized within a zero-correlation window, the ISI and MAI can be

reduced to zero. Thus, high system performance and capacity can be

ideally achieved.

Further, in LAS-TDD mode, all the signals will be kept within an

IFW via bi-synchronization. Fast power control is not needed, only slow

power control will be adopted to save power of mobile station. Therefore,

high mobility speed can be easily achieved.

Figure 4 shows the arrangement of the LS code within each time slot

of the LA code. The C and S codes of the LS code are positioned such

that the gap after the C code is the same as the gap after the S code

for all time slots except the last one. For the last time slot, the

4-chip gap is placed after the C code and another 4-chip gap is place

after the S code. That is the gap between C code and S code of the last

( 16^th) pulse must be 4 chips.

Figure 5 shows a LAS-TDD frame with distance gap and transition gap.

In Figure 5, a 24 ms LAS-TDD frame with a length of 30720 chips is given.

This frame consists of a 874 chips uplink sync subframe (SF) and a 962

chips downlink sync SF. The remaining space within the frame is divided

into 12 traffic SFs, each of a length of 2407 chips. In this frame,

half of the SFs are used for transmission and the other half for

reception. Transmit and receive SFs are organized in alternative order. Note that in a TDD system, in order to avoid the overlapping of receive

and transmit SF during the transmission path, gaps of unused chips must

be inserted after the transmit SF and before the receive SF. We call

this the distance gap. Further, a smaller transition gap must also be

placed after receive SF and before a transmit SF to allow sufficient

for the hardware to switch from a receiver to a transmitter. We call

this the switching gap. A framing method for the LAS-TDD frame and

allocating the gap space is described in the following.

1. Based on the required chip rate and frame length, determine the

number of chips interval per LAS-TDD frame. Let the number of chips

interval per LAS-TDD frame to be Tf. For chip rate equal to 1.28Mcps

and 24ms frame length. Thus, Tf = 30720 Tc, where Tc is the time interval

per chip.

2. Based on the required length of the uplink and downlink sync SFs,

determine the number of chip interval available for transporting

traffic SFs. Let Tu and Td to be the length of the uplink sync SF and

the downlink sync SF respectively. The number of chip intervals

available for traffic SF is Tt = Tf - Tu - Td. In the present embodiment,

Tu = 918 Tc and Td =918 Tc, thus Tt = (30720-918-918) Tc=28884 Tc.

3. Based on the length of the LA code, determine the number of traffic

SF that can be carried by the LAS-TDD frame. Let the length of the LA

code to be Ta, the number of traffic SF per LAS-TDD frame is Nt= Tt/Ta.

With reference Figure 1, the LA code with 16 pulses and length equal to 2387 Tc. Using the LA codes shown in Figure 1, the number of traffic

SFs per LAS-Tdd = 28884 Tc / 2387 Tc.

4. Based on the number of chip interval available for traffic SF

Tt and the number of traffic SF per LAS-Tdd frame Nt, determine the

number of chip interval allocated to each traffic SF. The number of

chip interval allocated to each traffic SF is Tsf = Tt / Nt. In the

present embodiment , Tsf - 28884/12 Tc - 2407 Tc.

Figure 5 shows a frame including a uplink sync SF of length of 918

chips, a downlink sync SF of 918 chips and 12 traffice SFs of length

of 2407 chips.

5. For each transmit SF, position the LA code n/2 chips from the

leftmost boundary of the SF. Also, allocate n/2 chips after the LA code

and before the distance gap. Where n is the transition gap required

after a receive SF and before a transmit SF.

6. For each receive SF, position the LA code n/2 chips from the

rightmost boundary of the SF. Thus, the distance gap between the

transmit SF and the receive SF can be determined as 2*(Tsf-Ta)-n.

Figure 6 shows a LAS-TDD frame with the downlink traffic to uplink

traffic ratio of 1:1. The LAS-TDD frame structure has chip rate of

1.28Mcps, frame length of 24 ms, LA code length of 2387 chips and both

uplink and downlink sync SF of 918 chips. The above framing method

can be further optimized. With reference to Figure 4, the gap between

the C and the S codes of the last time slots in the LA code can be reduced to 4 chips. Further, the gap after the S codes of the last time slots

in the LA code can be reduced to 4 chips. The remaining gap, which can

be reduced, after the S code in this time slots can be combined with

the distance gap to increase the length of the distance gap. That is,

the remaining 28 chips can be added to the distance gap after the LA

code. This significantly increases the distance gap and increase the

cell radius. Figure 7 shows another LAS-TDD frame with the downlink

traffic to uplink traffic ratio of 1:1. It is a equivalent diagram of

Figure 6 with the enlarged distance gap.

Figure 8 shows the relative position of the transmit and receive SFs

at different distances from the base station for downlink to uplink

traffic ratio of 1:1. In Figure 8, the transition gap is 1 chips. Thus,

4 chips at the end of the LA code is used as the transition gap. With

reference Figure 8, the 96 chips distance gap supports a cell radius

of 11.25 Km without any overlapping of the transmit and receive frame.

This cell radius provides a cell area of 397.6Km².

The above procedure can enlarge the distance gap between the

transmit SF and the receive SF. Such a framing method can generate

LAS-TDD frame for supporting alternating transmit and receive SFs,

inwhich the uplink and downlink traffic ratio is 1:1.

For a system with asymmetric traffic load, the number of required

downlink SFs is normally larger than that of uplink SFs. In such a

circumstance, the distance gap should be rearranged to achieve the maximum cell coverage.

The framing method for the LAS-TDD frame with a asymmetric traffic

load is described as follows.

1. Based on the definitions as described above, the available gap

space within the LAS-TDD frame is Tg= Tt-Nt*Ta, where Tt is the number

of chip intervals available for traffic SF, Nt is the number of traffic

SF per LAS-TDD frame, Ta is the length of the LA code. For Tt=28884

Tc, Nt = 12 and Ta = 2387 Tc, the available gap space Tg= 28884 Tc-

12*2387 Tc = 240 Tc.

2. Evenly divide this gap space among the transmit-to-receive

transition points. If every k downlink SF is followed by an uplink SF,

the number of transmit-to-receive transition point within the frame

is Nt/(k+l) and the number of chips per distance gap is (k+1) * Tg/Nt.

3. Based on the above-mentioned method, the length of the transmit

SF before the distance gap and the length of the receive SF after the

distance gap can be reduced. Thus, the distance gap can be increased

and the cell coverage area is enlarged.

Figure 9 shows the LAS-TDD frame for supporting a downlink to uplink

traffic ration of 2:1. This LAS-TDD frame is generated by the above

method where the 240 chips of gap space is first evenly divided among

the 4 transmit-to-receive transition points. Each transmit-to-receive

transition point is allocated 60 chips of distance gap. Then, the

distance gap optimization is applied such that 28 chips from the last transmit SF before the distance gap and 28 chips from the first receive

SF after the distance gap is re-assigned to the distance gap. Thus the

total length of the distance gap is 60+2*28=116 chips.

Figure 10 shows the relative position of the transmit and receive

SFs at different distance from the base station for downlink to uplink

traffic ratio of 2:1. The transition gap is 1 chip so that 4 chips at

the end of the LA code is used as the transition gap. As seen from Figure

10, 2*58 chips distance gap supports a cell area of 580.53 Km².

Note that the above description describes a framing method for

LAS-TDD frame with a length of 24 ms. However, the present application

is not limited to the 24 ms frame length and can be applied to various

frame lengths. In addition, different LA code length and downlink to

uplink transmission ratios can be used.

Figure 11 shows the transmission structure for the downlink sync

channel and uplink sync channel. In Figure 11, x is the timing advance

for the uplink synchronization.

Figure 12 shows the frame structure of the downlink sync channel.

The downlink sync channel maps to downlink sync SF to transmit a sync

code of a cell. Downlink sync channel assists the mobile station to

perform system acquisition, downlink sync, and channel estimation.

The length of a time slot is specified in Table 2. Each time slot

transmits one downlink sync burst of length 60 chips, which consists

of a pair of the 20-chip C section and the 20^~chip S section with a gap of 20 chips in between. The downlink sync burst is transmitted at

the beginning of each time slot.

Table 2 Time Slots of Downlink Sync Subframe

The sync codes may contain some system information, for example,

the LAS code for D-CPICH (Downlink-Common Pilot Channel).

Figure 13 shows a frame of the uplink sync channel. The uplink sync

channel is an uplink common physical channel that is used for the mobile

station to transmit uplink sync signals. The codes for uplink sync

channel are paired with the codes on ACPCH, and the available codes

and the relation between the codes of uplink sync channel and ACPCH

are broadcast on BCH.

The access burst, which consists of a 16-chip C section and a 16-chip

S section with a 16-chip gap in between, is transmitted with a time

offset ^k chips within the subframe. The C and S sections contain the

C code and S code of an LS code of 32 chips, respectively. The value

of the time offset ^k is taken from

A_k = (k 34 + l23)T_c, k = 0,1, 2,3,4,5.

Figure 14 shows the traffic subframe structure according to a

preferred embodiment of this invention.

The length of a traffic subframe is either 2387 chips or 2359 chips. The structure of a traffic subframe of 2387 chips, however, can be

derived from the structure of the traffic subframe of 2359 chips by

appending a 28-chip gap at the end. Hence, in this section, unless

otherwise stated, the structure of the traffic subframe of 2359 chips

shall be described.

The traffic subframe is divided into 16 time slots according to an

LA code. Each time slot, having a duration of at least 136 chips,

consists of a pair of the 64-chip C section and the 64-chip S section

with a gap of variable length appending to each section. The length

of gaps depends on the length of a time slot.

Figure 15 shows an example of LS Subsections of 64 chips. The C

section and S section can be equally divided into 2, 4, 8 subsections

of length 32 chips, 16 chips, 8 chips, respectively. The combination

of the n^th C subsection and the n^th S subsection is called the n^th LS

subsection. The length (in chip) of an LS subsection is defined as the

sum of the lengths of C subsection and the S subsection. Thus, an LS

section of 128 chips can be divided into either 2 LS subsections of

64 chips or 4 LS subsections of 32 chips or 8 LS subsections of 16 chips.

The traffic subframe is of two types: subframe type 1 and subframe

type 2.

Figure 16 shows a traffic subframe type 1. The subframe type 1 can

be used for downlink and uplink which includes pilot and physical layer

control information. An example of subframe of type 1 consists of 4 pilot bursts, as depicted in Figure 16. The four pilot bursts are

transmitted in time slots TS₀, TS₅, TS₁₀, and TS₁₅. The data bursts are

transmitted in the remaining time slots. The pilot burst and data bursts

are LS spread with same spreading code, but could have different

spreading factors.

A subframe of type 1 may transmit two or four control blocks, which

occupies an LS subsection of 64 chips each and are punctured in the

second LS subsection of 64 chips of pilot bursts. If two control blocks

are transmitted, they are transmitted in the second LS subsection of

64 chips of the second and third pilot bursts, i. e. time slots TS₀, TS₁₀.

Figure 17 shows the transmission of control blocks in a subframe of

type 1.

The transmission of control blocks in the subframe type 1 and the

spreading factor applied to the control blocks are negotiated at call

setup and can be re-negotiated during the call. They are indicated by

higher layer signalling. The control blocks are always transmitted

using the first code channel allocated in the subframe, according to

the order in the higher layer allocation message.

The traffic subframe type 1 may provide the possibility for

transmission of TFCI. (Transport Format Combination Indicatior) The

transmission of TFCI is done in the data parts of the respective

physical channel, this means TFCI and data bits are subject to the same

LS spreading with the LS same code as depicted in. The TFCI information is to be transmitted just before the second pilot burst and after the

third pilot burst, as shown in Figure 18.

The transmission of TFCI is negotiated at call setup and can be

re-negotiated during the call. It is indicated by higher layer

signalling, which TFCI format is applied. The TFCI is always

transmitted using the first subframe in a 24 ms frame and the first

code channel allocated in the subframe, according to the order in the

higher layer allocation message.

Figure 19 shows a traffic subframe type 2. The traffic subframe type

2 can be used for downlink and uplink which includes only data bursts.

All data symbols are subject to the same LS spreading with the same

LS code.

Table 3 shows the number of data symbols may be transmitted in a

subframe. However, the number of binary data transmitted by a subframe

depends on the spreading factor, modulation, and the number of the TFCI

bits.

Table 3 Number of data modulation symbols It will be apparent to those skilled in the art that various

modifications can be made to the present methods without departing from

the scope and spirit of the present invention. It is intended that the

present invention covers modifications and variations of the systems

and methods provided they fall within the scope of the claims and their

equivalents. Further, it is intended that the present invention cover

present and new applications of the system and methods of the present

invention.

Claims

1. A LAS-TDD framing method for physical layer of a wireless system,

in which a LAS-TDD frame comprises a downlink sync SF, an uplink

sync SF and traffic SFs, the method comprising the steps of:

calculating the number of chips per LAS-TDD frame based on chip

rates and frame length;

determining the number of chips for traffic SF by subtracting the

number of chips for downlink sync SF and uplink sync SF from the number

of chips per LAS-TDD frame;

characterized in that

determining the number of traffic SFs in the LAS-TDD frame and the

number of chips in each traffic SF based on the length of the LA code.

2. A method according to claim 1, characterized in that the traffic

SF is a transmit SF or a receive SF.

3. A method according to claim 1 or 2, characterized in that a

distance gap is inserted between the transmit SF and the receive SF.

4. A method according to claim 1 or 2, characterized in that a

transition gap is inserted from the leftmost boundary of the traffic

SF.

5. A method according to claim 1, 2 or 4, characterized in that a

transition gap is inserted between the LA code and a distance gap.

6. A method according to claim 5, characterized in that a transition gap is inserted from the rightmost boundary of the traffic SF.

7. A method according to claim 1, characterized in that reducing

the gap between the C and S codes of the last time slot in the LA code

to 4 chips.

8. A method according to claim 1 or 7, characterized in that reducing

the gap after the S codes of the last time slot in the LA code to 4

chips.

9. A method according to claim 7 or 8, characterized in that adding

the reduced gaps to the distance gap.

10. A method according to claim 5, characterized in that changing

distance gap based on the asymmetric ratio of the receive SF and

transmit SF.

11. A method according to claim 10, characterized in that reducing

the length of the transmit SF before the distance gap.

12. A method according to claim 11, characterized in that reducing

the length of the receive SF after the distance gap.

13. A method according to claim 1, where in the permutation position

of the LA codes can be recombined, and the permutation of a time slot

can be also recombined corresponding to it.

14. A method of claim 1, wherein the pulse polarity of the LA codes

can be transformed, and the polarity of a time slot can be also

transformed corresponding to it.