WIRELESS COMMUNICATION SYSTEM AND METHOD WITH SPATIAL INTERLEAVING

FIELD OF THE INVENTION

The present invention relates to a wireless communication system, to a method for wireless communication, to a radio transmitter and to a radio receiver.

BACKGROUND OF THE INVENTION

A wireless communication system typically comprises a radio transmitter and a radio receiver, wherein a RF (Radio Frequency) modulated signal transmitted from the transmitter reaches the receiver via a plurality of propagation paths. The parameters of these different propagation paths may vary in the time as well as in the frequency domains, such that a fading effect is imposed on the RF signal transmission.

A Multiple Input Multiple Output (MIMO) scheme is used for wireless communication system in order to provide a plurality of diversity paths against channel fading and to improve the system performance. Such a MIMO communication system requires multiple N _T transmit antennas and multiple N _R receiver antennas. A MIMO channel formed by N _T transmit antennas and N _R receiver antennas could be decomposed to Ns independent sub-channels, with N _s < min(Nτ N _R ).

Each of the Ns independent sub-channels can be referred to as a spatial sub-channel of the MIMO channel and corresponds to a dimension in mathematical expressions. Hence, a MIMO system can provide an improved performance if the additional dimensionalities created by multiple transmit and receive antennas are utilized. However, as channel parameters within wireless communication system may vary at all time and all Ns sub-channels are independent, the parameters of all Ns subchannels are not constants either. An Antenna Rate Control (ARC) technology can be used in a MIMO communication system in order to exploit all of the Ns sub-channels for data transmission. This is performed by dynamically assigning appropriate data transmission parameters (e.g. data rate, modulations mode, code rate, etc.) to each of the transmit antennas.

Fig. 5 illustrates a block diagram of a wireless communication system according to the prior art. In particular a ARC MIMO communication system is shown. Within a transmitter TX a data source DS is coupled to a de-multiplexed DEMUX, which de-multiplexes the data stream from the data source DS into N _T sub-stream each with a separate data rate T ₁ . (r ₀ , r _ls ...,r _N τ-i), where

N _τ -l r = ∑r,

(1)

Accordingly, the original data from the data source DS is assigned onto each N _T transmit antenna according to a rate controller RC. Then each sub-data stream is processed separately in an encoder and interleaving unit EI with control parameters, such as code rate, interleaving depth, modulation mode, etc.. Thereafter, the sub-data streams are forwarded to the RF channel via the transmitter units TMTR and N _T transmit antenna, respectively.

The receiver RX comprises N _R antenna for receiving mixed signals from the RF channel via receiving units RCVR for each antenna. All N _T sub-data streams are processed in a receiver space time processing unit RXP and are each forwarded to a de- interleaving and decoding unit DD. In a multiplexer MUX the sub-data streams are multiplexed , and are thus reassembled into a data stream with rate r.

US 2004/0196919 Al shows the transmission of an input stream in a MIMO wireless communication system with a plurality of transmitting antennas. The input data stream is de-multiplexed into sub-streams. Before transmitting the sub- streams via the transmitting antennas each of the sub-streams is modulated and coded to a maximum data rate.

However, the above MIMO communication systems merely uses a simple de-multiplex scheme to decompose the original user data stream with a rate r into N _T sub-data streams with rate r ₀ , r _ls ... r _N τ, respectively. Although each of the sub- data stream comprises some local interleaving processing, the inherent relationship among nearby bits in the original user data stream can not be completely eliminated. Therefore, if in several adjacent transmit antennas (i.e. adjacently numbered antennas) serious fading occur simultaneously and the interleave and code processing upon each corresponding antenna can not remove it, the sequential burst error after data stream reassembling may span too long to recover.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a wireless communication system and a communication method with an improved interleaving of an input data stream.

This object is solved by a communication system according to claim 1, a transmitter according to claim 8, a receiver according to claim 9 and a method for wireless communication according to claim 10.

Therefore, a wireless communication system is provided with a transmitter. The transmitter comprises at least one antenna for transmitting data; a spatial interleaving means for spatially interleaving a data stream to be transmitted into at least one sub-stream, and a rate controlling unit for controlling the data rates of the at least one sub-stream. The at least one sub-stream is transmitted via the at least one antenna.

Accordingly, the original data stream is scattered with onto the sub-data steams, which is compatible to different output rate according to the requirement of the rate controller. At the output of the spatial interleaving each bit keeps a considerable distance with nearby bits on both temporal and spatial domains.

According to an aspect of the invention the spatial interleaving means comprises a block interleaving unit for interleaving the data stream into a block matrix according to a spatial interleaving depth value, and an allocator unit for allocating the block interleaved data stream to the plurality of sub-streams by assigning the block interleaved data stream to a number of data input points corresponding to the spatial interleaving depth value and by separating the data input points into a number of groups according to the number of antennas. The allocator unit comprises at least one multiplexer for time-evenly multiplexing each group of data input points into a sub- stream.

According to a further aspect of the invention the transmitter comprises an forward error correction outer coder for performing an forward error coding on the data stream before the spatial interleaving means spatially interleaves the coded data stream.

According to still a further aspect of the invention the wireless communication system further comprises a receiver having at least one antenna for receiving at least one sub-stream of data; a spatial de-interleaving means for spatially

de-interleaving a sub-stream of data into a data stream, wherein the at least one sub- stream is received via the at least one antenna. Hence, a receiver is provided which can receive and decode the data stream transmitted by the transmitter.

The invention also relates to a transmitter for a wireless communication. The transmitter comprises at least one antenna for transmitting data; a spatial interleaving means for spatially interleaving a data stream to be transmitted into at least one sub-stream, and a rate controlling unit for controlling the data rates of the at least one sub-stream. The at least one sub-stream is transmitted via the at least one antenna.

The invention further relates to a receiver for a wireless communication. The receiver comprises at least one antenna for receiving at least one sub-stream of data; a spatial de-interleaving means for spatially de-interleaving a sub-stream of data into a data stream. The at least one sub-stream is received via the at least one antenna.

The invention also relates to a method for wireless communication. Data is transmitted data via at least one antenna. A data stream to be transmitted is spatially interleaved into at least one sub-stream. The at least one sub-stream is transmitted via the at least one antenna. The data rates of the at least one sub-stream are rate controlled.

The reason for the disadvantage encountered by the prior art is because the MIMO communication system only has conventional temporal interleaving upon each sub-data stream, but does not include any spatial interleaving for the whole data stream. When a serious burst fading takes place on the spatial domain and its influence exceeds the equivalent protection range on temporal domain, the error becomes unrecoverable.

The invention relates to a method of spatial interleaving among transmit antennas in rate control for in Antenna Rate Control (ARC) communication system, which may comprise Multiple Input Multiple Output (MIMO) such that spatial interleaving is introduced into the ARC MIMO communication system. Data stream(s) are interleave/de-interleave among multiple transmit antennas of the communication system to eliminate the inherent relation among nearby bits for the resistance on serious burst fading on the spatial domain. The MIMO system performance and capacity can be further improved by a combination with outer FEC (Forward Error Correction) coding/decoding. In other words, a spatial interleaving into an MIMO communication system is shown, which interleaves/de-interleaves data stream(s) among multiple transmit antennas to overcome the disadvantage mentioned above. During the spatial

interleaving into the MIMO communication system the original user data stream(s) is interleaved onto each sub-data streams corresponding to N _T transmit antennas instead of the simple de-multiplexing used by prior art MIMO systems. In particular, the original data stream is scattered with a certain pattern onto the N _T sub-data steams, which is compatible to different output rate according to rate controller's requirement. At the output of the spatial interleaving each bit keeps a considerable distance with nearby bits on both temporal and spatial domains. In another word, the inherent relation among nearby bits in original user data stream is eliminated on both temporal and spatial domains.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described in more detail with reference to the drawings.

Fig. 1 shows a block diagram of a wireless communication system according to a first embodiment of the invention; Fig. 2 shows a schematic block diagram of an allocator unit of the transmitter according to the first embodiment; Fig. 3A and 3B show schematic illustration of a spatial interleaving according to a second embodiment; Fig. 4 shows a schematic block diagram of an de-allocator unit of the receiver according to the first embodiment; and Fig. 5 shows a block diagram of a wireless communication system according to the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig. 1 shows a block diagram of a (wireless) communication system according to a first embodiment of the invention. This communication system relates to an antenna rate control ARC multi-input-multi-output MIMO communication system. The ARC MIMO communication system comprises a transmitter TX and a receiver RX. The transmitter TX comprises an outer encoder OE (optionally) receiving data as an input data stream from a data source DS, and a spatial interleaving unit SI for interleaving the outer encoded data stream into a number of sub-streams. An encoder and interleaving unit EI is provided for each of the sub-streams. Then each sub-data

stream is processed separately in an encoder and interleaving unit EI with control parameters, such as code rate, interleaving depth, modulation mode, etc.. The output from the encoder and interleaving units EI is coupled to a transmitter space time processing unit TXP. Thereafter, the sub-data streams are forwarded to the RF channel via the transmitter units TMTR and N _T transmit antenna ATO, ..., AT _{NT I} , respectively.

The receiver RX comprises N _R antenna ARO, ..., AR _N τ i, for receiving mixed signals from the RF channel via receiving units RCVR for each antenna. All N _T sub-data streams are processed in a receiver space time processing unit RXP and are each forwarded to a de-interleaving and decoding unit DD. In a spatial de-interleaver unit SDI the sub-data streams are de-interleaved , and are thus reassembled into a data stream with rate r.

A more detailed description on a MIMO wireless communication architecture can be found in 3GPP TR 25.876, "Multiple-Input Multiple-Output Antenna Processing for HSDPA"; and in Lucent, "Enhancements for HSDPA Using Multiple Antennas". TSGRl#15(00)1096, 22nd-26th, August 2000, Berlin, Germany, which are both incorporated herein by reference.

A MIMO channel formed by N _T transmit antennas and N _R receiver antennas can be decomposed to Ns independent sub-channels, with N _s < min(Nτ N _R ). A more detailed description on these Ns independent sub-channels can be found in Lucent, Nokia, Siemens, Ericsson. "A standardized set of MIMO radio propagation channels". TSGR1#23(O1) 1179, 19-23rd, November, 2001, Jeju, Korea as well as in 3GPP TR 25.996, "Spatial Channel Model for Multiple-Input Multiple Output Simulations", which are both incorporated herein by reference.

An Antenna Rate Control ARC technology is used in the above MIMO communication system in order to exploit all of the Ns sub-channels for data transmission. A more detailed description of the ARC technology in a MIMO communication system can be found in Lucent, "Increasing MIMO throughput with per-antenna rate control" TSGRl (01)0879, 27th-31st August, Turino, Italy, which is incorporated herein by reference.

Accordingly, the simple de-multiplexer and multiplexer on transmit and receive sides in a prior art ARC MIMO system are replaced with spatial interleaver and de-interleaver respectively. In addition, before/after the spatial interleaver/de- interleaver, an additional outer FEC coder/decoder is provided, which is independent to

all coding/decoding modules upon all sub-data streams. Such a system structure with spatial interleaving and corresponding outer FEC coding can effectively resist serious fading upon nearby antennas and correct errors that separate FEC coding on each antenna can not achieve.

The spatial interleaving method will now be described in more detail.

If sub-data stream rates { ^r > }, ^r > ^{€ N} ' ^{l =} °' ^{1? ' " N} τ ^~ ^ _are applied upon N _T transmit antennas based on rate control results in the transmit side, the original data rate r and sub-data stream rates Jr ₁ } will meet equation (1).

First step is to find the greatest common divisor c of all {rj,

' ' ^~~ ' ' ^τ with algorithm described with ANSI C language as below:

for ( i = 0, i < N ₁ . - 1 , i ++ )

{ whi le ( r _t I= r _i+l )

{ if ( r, < r _ι+λ ) ^r ₁₊ ι = i+l - r else r = r - r :+l '

C = V

The above algorithm for the greatest common divisor c is used to avoid any inconvenient division calculations in a hardware device.

After deducing the greatest common divisor c of all { ^r > } ,

^ e NJ = OX-N ₁ - I , the spatial interleaving depth can be determined by

based on equation (1), the equation (2) could also be expressed as

M = β - - (3) c

wherein the integer parameter β, β e N is configured to adjust the spatial interleaving depth: The larger β the deeper interleaving but more interleaving/de-interleaving delay and hardware resource on both transmit and receive sides are required. Accordingly, the value of β is based on a trade-off between system performance and implementation complexity.

Based on the spatial interleaving depth M, the original data stream is firstly block- interleaved in a M xM matrix buffer as: m° ^ut = m ^m _{i i} z = 0,l,- - -, M xM - I (4)

Af (imodλ/)+ —

The m'" represents the input sequence to interleaving buffer, and m° ^ut corresponds to the output sequence from the buffer. After the block interleaving with depth M , the original input data stream { b _t } , i = 0,1, • • • ,M xM - 1 is mapped to

V ^U 0 ' ^υ M ' ^ 2Af ' ^{' ' '} ' V(M-V) M ^■ > ^U l ^■ > ^U M+l ' ^2Af +1 ' ^{' ' '} ' ^U (M-V) Af +1 ' "MxM-M-I ' "MxM-I )

Fig. 2 shows a schematic block diagram of the spatial interleaver SI according to the first embodiment. The spatial interleaver SI comprises a block interleaver BI and an allocator unit AU. As the last step of spatial interleaving, the block-interleaved results from the block interleaver BI should be allocated by the allocator unit AU.

In the allocator unit AU, blocked interleaved data stream b is time-evenly cyclically assigned to M data input points bit by bit. These M data input points are

T separated to N _T 1 groups. Each group contains β • — data input points and all c

T these β • — data input points are connected to one multiplexer MUX. All multiplexer c

T

MUX respectively multiplexes β • — input data time-evenly and concurrently sent c respective multiplexed data sequence with the pre-determined output data rate T ₁ . The mapping should correspond to

∑ $ — ∑ β — Af+∑ β - M +∑ β -J- Af(Af-l)+£ β ^ Af(Af-l)+£ β ^

i = 0,l, — N _T - l (6)

Based on this spatial interleaving method, the minimum distance between any bits transmitted simultaneously on any two antennas is

(V)

C

Accordingly, equation (7) may be utilized as a criterion for the value the parameter β.

On the receiver side RX , the spatial de-interleaver performs all inverse processing to de-interleave all sub-data streams to their original order. Then the de- interleaved data stream is sent to outer decoding part for outer FEC.

The suggested spatial interleaving method could be implemented by hardware/software with common devices, such as block- interleaver/de-interleaver, multiplexer/de-multiplexer and some simple calculation modules.

Fig. 3A and 3B show schematic illustration of a spatial interleaving according to a second embodiment. Here, an example of the spatial interleaving method is described for a dual antennas ( N ₁ , = 2 ) ARC MIMO communication system according to the second embodiment. The rate controller RC implements a configuration of dual antennas as shown in the table 1 :

According to above greatest common divisor algorithm the greatest common divisor of ro and x _\ can be deduced as c=2. If β = 3 , the spatial interleaving depth M according to equation (2), will correspond to M=9.

The input original data stream {b _t } i = 0,1, • • • ,80 is block- interleaved in a 9x9 buffer according to equation (4). The output of the 9x9 block interleaving corresponds to b _o ,b _g ,- - -,b ₁₂ ,b _l ,b _w , ,b _% ,b _λl ,- - -,b _m .

Thereafter, the output of the block interleaving is allocated to dual antennas as described by equation (6), i.e. each 3 and 6 consecutive bits are allocated to antenna ATI and antenna AT2 alternately. The final spatial interleaving result is shown in Fig.3B. Accordingly, the minimum distance between bits in spatial domain after the interleaving is D _min =27.

Fig. 4 shows a schematic block diagram of the spatial de-interleaver SDI in a receiver RX according to the first embodiment. The spatial de-interleaver SDI comprises a block de-interleaver BDI and an de-allocator unit DAU. The received sub- streams are de-multiplexed and are forwarded to the block de-interleaver which performs a block de-interleaving on these data.

The de-allocator unit DAU comprises a plurality of de-multiplexers DEMUX each for de-multiplexing the concurrently received sub-streams with data rate X ₁ into data output points. The output data points are block de-interleaved by the block de-interleaver BDI into a data stream. Accordingly, the spatial de-interleaver SDI performs an inverse processing compared to the spatial interleaver of Fig. 2

Although the above embodiments have been described with reference to an ARC MIMO communication system, the basic principles of the invention may be implemented in other multiple antenna systems, such as SIMO (Single Input Multiple Out), andMISO (Multiple Input Single Output) systems.

The above described spatial interleaving can be implemented with current available hardware such that no special device is required.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps other than those listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. In the device claim enumerating several means, several of these means can be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually

different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Furthermore, any reference signs in the claims shall not be constrained as limiting the scope of the claims.