HK1080225A - Interleaving of information bits - Google Patents

Description

Interleaving of information bits

Technical Field

The present invention relates to wireless communications. In particular, the present invention relates to interleaving of information bits for transmission over a wireless interface. The invention is also applicable to de-interleaving (de-interleaving) of received information bits.

Background

Communication systems are known in which a wireless interface is provided for an entity provided with a transmitter and/or a receiver. The entities may comprise devices such as mobile or fixed user equipment (e.g. mobile phones), base stations provided with transmitters and/or receivers and/or other devices. The communication over the wireless interface may include, for example, communication of voice, data, multimedia, etc.

A communication system typically operates in accordance with a given standard or specification which sets out what the various components of the system can do and how that should be done. For example, the standard or specification may define whether a user, or more precisely a user equipment or terminal, is provided with a circuit switched service and/or a packet switched service. Communication protocols and/or parameters to be used for the connection may also be defined. A hierarchical order of the various functions associated with the communication instances may also be defined. In other words, a specific set of "rules" on which the communication can be based needs to be defined to enable communication through the system.

An example of wireless communication is a Public Land Mobile Network (PLMN). A PLMN is a cellular system in which a Base Transceiver Station (BTS) or similar entity of a radio access network of the communication system provides services to User Equipment (UE), such as Mobile Stations (MS), over a wireless interface between these entities. A more specific example of such a so-called second generation (2G) PLMN system is the global system for mobile communications (GSM).

A further development of GSM is the so-called enhanced data rates for GSM evolution (EDGE). EDGE is a standard prepared by the third generation partnership project (3GPP) and is now also defined by ETSI (european telecommunications standards institute). A description of GSM/EDGE radio access networks (GERAN) and channel coding for GERAN can be found, for example, from the 3G specification TS45.003 v5.5.5 (2002-04).

EDGE can achieve higher data rates than conventional 2G GSM. Such improvements, which are included in various other modifications, are achieved by making changes in the modulation.

GERAN is based on using TDMA (time division multiple access) transmission. In TDMA-based systems, transmissions are made in time frames. Each frame may be divided into a plurality of slots. Dividing a frame into a plurality of slots allows multiple users to share the frame. A TDMA frame may be viewed as a physical channel that provides a communication medium for the transfer of information between two nodes of a communication system. The time slots may be used for successive frames to form a physical channel for transmission. A burst (burst) is then transmitted in each time slot.

A typical TDMA transmitter will include means for performing channel coding, interleaving, burst formation, modulation and actual transmission, see fig. 1. It should be understood that these functions may be provided by means of separate entities, or at least some of these functions may be provided by means of functional blocks of the transmitter.

After channel coding, the information bits form an entity called a block. The total number of bits in a block depends mainly on the chosen encoder. A block is typically transmitted over multiple bursts (i.e., over multiple consecutive frames) in one time slot.

The information bits in a block are spread to the appropriate positions in the burst by means of interleaving. The goal is typically to distribute successive information bits as far apart as possible from each other. In the above technical specification 3GPP TS45.003, a diagonal interleaver (diagonalinterleaver) is given for processing a block of 456 coded bits. The block of encoded data is the interleaver "block diagonal", where a new block starts every 4 blocks and the data is distributed over 8 blocks. In a given interleaver:

455 is equal to 0, 1, 2

b＝k mod 8

Where j is the position of bit k in burst b.

If we name J as burst size (114 in the example below), K is block size (456), O is ordering parameter (49) and D is interleaving depth (8), equation (1) can be written as:

k-1 for K ═ 0, 1, 2

b＝kmod D

Note that:

it can be considered that: this formula works well as long as half the block size (K/2) cannot be divided by the interleaving depth (D). This can be achieved as long as the block size K is larger than the interleaving depth D, i.e.:

equation (3) can check whether the interleaving equation (2) works. In the above example, equation (3) would give ((456/2) mod8) ═ 4.

Communication systems typically have individual functions. As explained above, the functions may be hierarchically divided into a plurality of groups. These are often referred to as layers. Typically, the lowest layer in a layer stack will comprise the actual physical transmission medium, i.e. the logical traffic channels providing the radio bearer for transmission. This is commonly referred to as the physical layer. One or more layers above the physical layer contain functions such as radio link control, medium access control (MAC: a sub-layer of the radio interface layer 2 that provides unacknowledged data transfer traffic on logical channels and access to transport channels). Since only the physical layer is of interest in understanding the present invention, no further discussion of the other layers is made herein.

The Flexible Layer One (FLO) for GERAN has been proposed in the third generation partnership project (3GPP) standardization. This is a new configurable physical layer for GSM/EDGE radio access networks (GERAN). The advantage of the proposed new physical layer is that functions such as channel coding, interleaving etc. can be specified during the call setup phase. This then means that new services, such as Internet Protocol (IP) multimedia subsystem (IMS) services, can be supported without requiring the specification of new coding schemes. Moreover, the physical layer may be more consistent with that specified by the third generation (3G) Universal Mobile Telecommunications Service (UMTS) terrestrial radio access network (UTRAN).

The present inventors have found that existing diagonal interleavers such as those described above are not easily reused for this purpose, and to implement this scheme, a new type of diagonal interleaver needs to be specified. The reason for this is that the scheme frees up bits for transmitting information.

There are then some unresolved problems with this regard. Most importantly, existing diagonal interleavers can no longer work in all cases, for example, since 3GPP schemes enable the case where half the block size can be divided by the interleaving depth. That is, when the above relation (3) is no longer satisfied, that is:

the interleaving equation (2) does not work any more. This becomes a problem because there are no more than the first 57 information bits, the scheme enables the transmission (and thus interleaving) of block sizes of 58 bits and 464 bits (equal to 4 bursts). This results in ((464/2) mod8) being 0, i.e., the above-mentioned case where the condition (3) is not satisfied.

This problem is illustrated by the following simple example of the case where the relation (3) is not satisfied. Suppose that:

k is 16 blocks in size

J-4 burst size

1 ordering parameter

D-8 interleaving depth

It is possible to check by (3) that true ((16/2) mod8) ═ 0, and the condition (3) is not satisfied accordingly. Table 1 shown in fig. 4 lists values given by the interleaving formula (2) for the above specific example. As shown by table 1, starting from the 8 th bit, the interleaving equation (2) no longer works properly, since:

the 8 th bit maps to the same position and the same burst as the 0 th bit;

the 9 th bit maps to the same position and the same burst as the 1 st bit;

the 10 th bit maps to the same position and the same burst as the 2 nd bit;

the 11 th bit maps to the same position and the same burst as the 3 rd bit;

-the 12 th bit maps to the same position and the same burst as the 4 th bit;

-the 13 th bit maps to the same position and the same burst as the 5 th bit;

the 14 th bit maps to the same position and the same burst as the 6 th bit;

the 15 th bit maps to the same position and the same burst as the 7 th bit.

This may cause various problems in the transmission and reception of bits.

Disclosure of Invention

Embodiments of the present invention are intended to address the above-described problems associated with interleaving in the examples to avoid improper mapping of information bits in bursts.

According to one aspect of the present invention, there is provided a method in a transmitter for interleaving information bits from a data block into transmission bursts, each information bit being assigned an index, the interleaving comprising calculating the position of the information bits in the transmission bursts such that the value of the index of at least a part of the information bits is modified.

The modification of the exponent value may include biasing the exponent value by a bias term. Each information bit to be included in one of the transmission bursts may be provided with an exponent number, and the sum of the exponent number of each information bit and the offset term may form the modified value of the exponent of the information bit used in the calculation.

In a further embodiment, it is determined whether the value of the index needs to be modified. The determination may include determining whether half of the block size is divisible by the interleaving depth.

According to another aspect of the present invention, there is provided a method in a receiver for deinterleaving information bits from a received transmission burst, each information bit being assigned an index, the deinterleaving comprising: determining whether a value of any index is modified prior to transmitting the transmission burst; and deinterleaving the information bits according to the modified value of the exponent or the original assigned value of the exponent based on the determination.

According to another aspect of the present invention, there is provided a transmitter comprising:

an interleaver for interleaving information bits from the data block into transmission bursts, each information bit being assigned an index; and

means for calculating the position of the information bits in the transmission burst, thereby modifying the value of the exponent of at least a portion of the information bits prior to the interleaving.

According to another aspect of the present invention, there is provided a receiver comprising:

a deinterleaver for deinterleaving information bits from the received transmission burst, each information bit being assigned an index; and

means for determining whether any of the exponents was modified prior to transmission of the transmission burst, the deinterleaver being arranged to deinterleave the information bits in accordance with the modified value of the exponent or the original assigned value of the exponent based on the determination.

Embodiments of the present invention may provide means to avoid mapping too many information bits onto locations in a burst. Diagonal deinterleaving is possible even under the condition that equation (3) above is not satisfied.

Drawings

For a better understanding of the present invention, reference will now be made, by way of example, to the accompanying drawings, in which:

fig. 1 schematically shows a transmitter arrangement in which the invention can be applied;

fig. 2 schematically shows a receiver apparatus in which the invention may be applied;

FIG. 3 is a flow chart of an embodiment;

FIG. 4 shows a table of values obtained from an interleaving formula according to the prior art; and

fig. 5 shows a table of values obtained by an interleaving formula according to an embodiment of the present invention.

Detailed Description

Fig. 1 schematically depicts certain components of a typical TDMA transmitter. More specifically, fig. 1 shows a channel encoding block 8, an interleaving block 10, a burst information block 12, a modulation block 14, and a transmission block 16 in the direction of signal flow through the transmitter. The transmission block or radio block 16 is typically followed by a suitable antenna arrangement 18. Since the present invention relates to the operation of the interleaving block 10 and since the purpose and operation of the other blocks are familiar to a person skilled in the art, it will not be described any further here.

Fig. 2 schematically depicts certain components of a typical TDMA receiver. More specifically, fig. 2 shows the receiving block 24, the modulation block 22, the de-interleaving block 20 and the channel decoding block 18 in the direction of the information signal flow through the receiver, which is received by means of a suitable antenna arrangement. As above, no further explanation of the purpose and operation of blocks 18, 22 and 24 is necessary.

Fig. 3 is a flow chart according to an embodiment of the present invention. In operation, the interleaving block 10 is arranged for interleaving information bits from a data block into transmission bursts. Each of the information bits is assigned an index (index). Exemplary values of the index are shown in column k of the tables of fig. 4 and 5.

During interleaving, the position of the information bits in the transmission burst is calculated. In accordance with the principles of the invention, the position is calculated based on a modified value of the exponent of at least some of the information bits.

Referring now also to fig. 5, shown is table 2 of values obtained by an embodiment of the present invention.

The parameters in table 2 of fig. 5 correspond to the parameters in table 1 of fig. 4, except that the value of parameter j is obtained by using the modified equation (2) of diagonal interleaving. More specifically, an offset term (shift term) s is introduced in the formula (2).

The use of the new item s can be described in more detail as follows:

k-1 for K ═ 0, 1, 2

b＝kmod D

If it is notThen

Otherwise s is 0

Where j is the position of bit k in burst b.

The offset term s is only activated when half the block size can be divided by the interleaving depth (see (4) above). In the above example, the offset term s is 0 for the first half block and 1 for the second half block.

The value 4 represents the size of a radio block. In the given example, the radio block consists of 4 bursts. If a different radio frequency block is used, the value should change accordingly.

The calculation for obtaining the value of parameter j in table 2 is based on equation (2) above, except for the introduction of an offset term, and is done with the values as used in the example above. It is easy to note that because of the offset term s, the bits are no longer mapped twice in the same position in the interleaving stage (as is the case for bits 0 and 8, 1 and 9, 3 and 11, etc. in table 1).

When receiving a signal, for example by the receiver apparatus of fig. 2, the de-interleaving block should use the same rules as above. For example, the de-interleaving block 20 knows that the exponent may have been modified and therefore checks the received burst. The value of the block may explicitly indicate to the receiver whether a modification such as an exponential offset has been used.

It should be understood that the index does not necessarily have to consist of numbers. The index value may be given by a character or a string of characters, for example. The string may include, for example, letters, or a combination of letters and numbers.

It should also be appreciated that although the present invention has been described in connection with user equipment of a PLMN system, embodiments of the present invention may be applied to any other suitable type of communication system comprising transmitter and receiver equipment.

Embodiments of the present invention have been described in the context of GSM/EDGE and TDMA systems. The invention is also applicable to any other communication system and access technology where applicable. Examples of other access technologies include code division multiple access, frequency division multiple access, space division multiple access, and any mixture thereof.

It is also noted herein that while the above describes exemplifying embodiments of the invention, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention as defined in the appended claims.

Claims (10)

1. A method in a transmitter for interleaving information bits from a data block into transmission bursts, each information bit being assigned an index, the interleaving comprising calculating the position of the information bits in the transmission bursts such that the value of the index of at least a part of the information bits is modified.

2. A method as claimed in claim 1, wherein the modification of the exponent comprises shifting the value of the exponent to be modified by a shift term.

3. A method as in claim 2, wherein each information bit to be included in one of the transmission bursts is provided with an index number, and the sum of the index number of each information bit and the offset term forms a modified value of the index of said information bit to be used in the calculation.

4. A method as claimed in any preceding claim, comprising determining whether a modification of the value of the index is required.

5. The method of claim 4, wherein said determining comprises determining whether half the size of the data block is divisible by the interleaving depth.

6. A method as in claim 5, if a parameter associated with interleaving satisfies a criterionWherein:

k is the data block size given in bits, D is the interleaving depth given as the number of bursts,

modifying the value of the exponent of the information bit by an offset term s, said term being obtained by the following formula:

wherein

k is the value of the exponent of the information bit.

7. A method as in any preceding claim, wherein the transmitter is for transmitting in a GSM/EDGE radio access network.

8. A method in a receiver for deinterleaving information bits from a received transmission burst, each information bit being assigned an index, the deinterleaving comprising:

determining whether a value of any index is modified prior to transmitting the transmission burst; and

deinterleaving the information bits according to the modified value of the exponent or the original assigned value of the exponent based on the determination.

9. A transmitter, comprising:

an interleaver for interleaving information bits from the data block into transmission bursts, each information bit being assigned an index; and

means for calculating the position of the information bits in the transmission burst, thereby modifying the value of the exponent of at least a portion of the information bits prior to the interleaving.

10. A receiver, comprising:

a deinterleaver for deinterleaving information bits from the received transmission burst, each information bit being assigned an index; and

means for determining whether any of the exponents was modified prior to transmission of the transmission burst, the deinterleaver being arranged to deinterleave the information bits in accordance with the modified value of the exponent or the original assigned value of the exponent based on the determination.