GB2364220A

GB2364220A - Encoding information in midamble shifts

Info

Publication number: GB2364220A
Application number: GB0015669A
Authority: GB
Inventors: Stamatis Kourtis
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 2000-06-28
Filing date: 2000-06-28
Publication date: 2002-01-16
Also published as: AU6748101A; GB0015669D0; WO2002001789A1

Abstract

The present invention is suitable for use with communications systems which combine Spread Spectrum and Time Division technologies, for example UTRA TDD. In such systems data is transmitted in bursts, each burst including a set of spreading codes and a midamble. However only a subset of the spreading codes may be active. In the present invention the midamble is coded with midamble shifts which provide an indication of which spreading codes are active. A signalling scheme is employed in which a transmitted midamble is shifted by first, S<SB>1</SB>, and second, S<SB>2</SB>, pointer signals which signal respectively the last code belonging to the subset of active codes and the number of codes in the original set which are not in the active subset. This provides the following advantages: not only does the receiver know the number of active codes, but also it knows (as indicated by the first midamble shift) which of the original set of codes it has to search in order to find the active codes. In order to reduce possible ambiguities a third shift, S<SB>3</SB>, may be used to indicate whether the number of codes in the set is even or odd.

Description

2364220 RADIO COMMUNICATION SYSTEM, TRANSMITTER AND RECEIVER

Field of the Invention

This invention relates to radio communication systems and particularly to such systems employing midamble coding.

Background of the Invention

In the field of this invention it is known (for example from the technical specification '3 G TS 25 221 V 3 2 0 ', released in March 2000, of the '3rd

Generation Partnership Project, Technical Specification Group Radio Access

Network', relating to physical channels and mapping of transport channels onto physical channels using time division duplex (TDD) techniques) to allocate midamble portions of transmissions (more commonly referred to simply as midambles') for physical channels.

In general, midambles are part of the physical channel configuration which is performed by higher layers in a layered, hierarchical data management scheme.

Optionally, if no midamble is allocated by higher layers, a default midamble allocation may be used This default midamble allocation is given by a fixed association between midambles and channelisation codes, and is applied individually to all channelisation codes within one time slot Different associations apply for different burst types and cell configurations with respect to the maximum number of midambles.

In the case of midamble allocation for down-link (DL) physical channels, physical channels providing a beacon function always use reserved midambles For all other DL physical channels the midamble allocation is signalled or given by default.

In the case of midamble allocation by signalling, either a common or a user- equipment (UE) specific midamble is signalled to the UE as a part of the physical channel configuration.

If no midamble is allocated by signalling, the UE derives the midamble from the associated channelisation code and uses an individual midamble for each channelisation code For each association between midambles and channelisation codes if no midamble is allocated by higher layers, there is one primary channelisation code associated to each midamble A set of secondary channelisation codes is associated to each primary channelisation code All the secondary channelisation codes within a set use the same midamble as the primary channelisation code to which they are associated.

Higher layers allocate the channelisation codes in a particular order Primary channelisation codes are allocated prior to associated secondary channelisation codes If midambles are reserved for the beacon function, all primary and secondary channelisation codes that are associated with the reserved midambles are not used.

Primary and respective associated secondary channelisation codes are not allocated to different UE's.

In the case that secondary channelisation codes are used, secondary channelisation codes of one set are allocated in ascending order, with respect to their numbering.

If the midamble is part of the physical channel configuration, an individual midamble is assigned to all UE's in one time slot If no midamble is allocated by higher layers, the UE derives the midamble from the assigned channelisation code as for DL physical channels.

The current specification for UTRA TDD (Time Division Duplex mode of

Universal Mobile Telecommunications System Terrestrial Radio Access of the European Telecommunications Standards Institute (ETSI)) does not provide the means to signal to the mobile terminal what are the active codes for the case of the common midamble.

It has been proposed that, for the case of the common midamble, multiple midamble shifts be used in order to signal to a mobile station the number of currently active codes used in a time slot.

However, this approach has the disadvantage(s) that, nonetheless, the mobile station has to search over the whole set of, say 16, codes in order to detect which are the active ones.

It is an object of the present invention to provide a radio communication system and method therefor wherein the abovementioned disadvantage(s) may be alleviated.

Statement of Invention

In accordance with a first aspect of the present invention there is provided a radio communication system as claimed in claim 1.

In accordance with a second aspect of the present invention there is provided a transmitter for a radio communication system as claimed in claim 6.

In accordance with a third aspect of the present invention there is provided a receiver for a radio communication system as claimed in claim 11.

Brief Description of the Drawing(s)

One radio communication system, method and incorporating the present invention will now be described, by way of example only, with reference to the accompanying drawing(s), in which:

FIG 1 shows, in a transmitter of a system employing a midamble coding scheme for UTRA TDD data transmission in a timeslot, a block diagram illustrating shifting of the midamble; and FIG 2 shows a block diagram illustrating, in a receiver, recovery of midamble shift information to facilitate decoding of the midamble.

Description of Preferred Embodiment(s)

Referring now to FIG 1, in a transmitter 100 of a system employing a midamble coding scheme for UTRA TDD data transmission using a set of codes with sufficient cross-correlation properties in order to realise multiple user detection In the transmitter 100, a midamble for transmission in a timeslot is passed through a shifter 110, which applies to the midamble a first shift S, (whose significance will be explained in greater detail below), controlled by an S, input The resultant Si- shifted midamble is then passed through a shifter 120, which applies to the midamble a second, compound shift 52 (whose significance will also be explained in greater detail below), controlled by an 52 input Finally, the resultant (S, 52)-shifted midamble is then passed through a shifter 130, which applies to the midamble a third, compound shift 53 (whose significance will also be explained in greater detail below), controlled by an 53 input The resultant composite (S,, 52, 53)- shifted midamble is then passed to additional processing elements (not shown) for transmission.

As will be understood, in UTRA TDD transmission the composite midamble may be coded using the sixteen predetermined midamble shift positions (or a subset of them according to the system configuration) (for 'burst type 1 ' transmission) or the six predetermined midamble shift positions (or a subset of them according to the system configuration) (for 'burst type 2 ' transmission) It will also be understood that, in choosing the active subset, the codes are allocated in a certain manner, i e,the resource manager assigns codes from top to bottom For example, in a particular burst type 1 ' transmission there may be six codes which form the subset of active codes, and which are spread over the first ten of the possible sixteen codes (e g, the 1st, 2nd, 5 h, 8 Ch, 9 Th and 10 codes of the sixteen available).

As will be explained in further detail below, in order to facilitate the detection of the active channelisation codes, the midamble is coded to signal to the receiver not just the number of channelisation codes used in the DL timeslot, but also further information on the channelisation codes used which allows the receiver to know over which subset of available codes it must search in order to find the active codes used.

The first shift S, is chosen to be equal to the very last code (of the sixteen available) that is used in the subset of active codes The second shift 52 is chosen to be equal to the number of codes not used in the active subset Thus, it will be appreciated that in the above example (where there are six codes which are active, and which are spread over the first ten of the possible sixteen codes) the first shift S, would have a value of 10, and the second shift 52 would have a value of 4 (= 10-6) Thus it will be appreciated that the shift values S, (= 10) and 52 (= 4) act as pointers to the 10 ' code (the last code of the active set) and the 4 code from the available sixteen.

It will be understood that the fact that the pointer or shift values S, and 52 indicate (in addition to the number of codes in the active set) which subset of the available sixteen codes must be searched in order to find the active codes allows significant improvement in both the error performance of the code detection procedure and its computational complexity, thus allowing code detection to be performed more quickly and/or with less power consumption.

It will be appreciated that the code signalling scheme described above is readily applicable to 'type burst 1 ' transmissions when the channel length is relatively short in order to support sixteen midamble shifts Nonetheless, it will be understood the scheme is equally applicable for longer channel lengths and also for 'type burst 2 ' transmissions However, although some uncertainties could arise with use of these transmissions (i e, where the S, and/or 52 values may utilise different mapping and/or encoding to identify unambiguously precisely how many codes are in the active set), this uncertainty could be eliminated by the introduction of a third midamble shift 53 which is a single binary value and acts as a flag to indicate for example whether the number of active codes is even or odd.

Referring now to FIG 2, in a receiver 200 a received, coded midamble is extracted from the received burst and passed through a first shift detector 210 which detects the first shift S, present in the received midamble The detected shift value S, is passed to processing circuitry (e g, a microprocessor) 240.

The midamble from the first shift detector 210 is passed through a second shift detector 220 which detects the second shift 52 present in the received midamble The detected shift value 52 is passed to the processing circuitry 240.

The midamble from the second shift detector 220 is passed through a third shift detector 230 which detects the third shift 53 present in the received midamble The detected shift value 53 is passed to the processing circuitry 240.

The processing circuitry 240 receives the received burst, together with the shift values S,, 52 and 53 from the first, second and third shift detectors 210, 220 and 230 For the cases when the 53 flag is utilised, the 53 value is logically combined with the S, and/or 52 values from the first and/or second shift detectors to produce expanded S, and/or 52 values which unambiguously indicate respectively the ending code number and the number of the codes in the active set The processing circuitry subtracts the 52 value from the S, value to produce a difference value (in the present example, = 6, derived 51 = 10 and 52 = 4) The value is thus equal to the number of codes in the active set The processing circuitry 240 then searches the (= 6) codes within the subset of the sixteen available codes, starting with the code 1 and ending with the code 51 (= 10) When the active code set is determined, it is passed to the demodulator circuitry (not shown) in order to perform the data extraction from the received burst.

It will be understood that in this way the processing circuitry 240 has only to search for six codes within the subset of ten codes in order to be able to determine the appropriate six channelisation codes, allowing significant improvement in both the error performance of the code detection procedure and its computational complexity, thus allowing code detection to be performed more quickly and/or with less power consumption.

Claims

Claims

1 A radio communication system for coding a midamble with one of a subset of a predetermined set of midamble shift positions, the system comprising:

in a transmitter, means for coding the midamble in accordance with both the number of the active codes and a subset of the total possible codes, which subset includes all active codes; means for applying to the midamble a first shift representative of a first signal indicative of the position in the predetermined set of the final code of the active set; and means for applying to the midamble a second shift representative of a second signal indicative of the number of codes which are not in the active set, and in a receiver, means for recovering from a received midamble the first signal indicative of the position in the predetermined set of the final code of the active set; means for recovering from the received midamble the second signal indicative of the number of codes which are not in the active set; and means for determining from the recovered first signal and the recovered second signal the set of active codes.

2 The system according to claim 1 wherein the system is arranged for UTRA TDD data transmission.

3 The system according to claim 2 wherein the system is arranged for type burst 1 UTRA TDD data transmission.

4 The system according to claim 1 or 2 wherein:

the transmitter further comprises means for applying to the midamble a third shift representative of a third signal indicative of whether the number of codes in the subset is odd or even, the receiver further comprises means for recovering from the received midamble the third signal indicative of whether the number of codes in the N subset is odd or even, and the means for determining is arranged to determine the set of active codes from the recovered first signal, the recovered second signal and the recovered third signal.

The system according to claim 4 wherein the system is arranged for type burst 1 UTRA TDD data transmission or type burst 2 UTRA TDD data transmission.

6 A transmitter for use in a radio communication system for coding a midamble with one of a subset of a predetermined set of midamble shift positions, the transmitter comprising:

means for coding the midamble in accordance with both the number of the active codes and a subset of the total possible codes, which subset includes all active codes; means for applying to the midamble a first shift representative of a first signal indicative of the position in the predetermined set of the final code of the active set; and means for applying to the midamble a second shift representative of a second signal indicative of the number of codes which are not in the active set, 7 The transmitter according to claim 6 wherein the transmitter is arranged for UTRA TDD data transmission.

8 The transmitter according to claim 7 wherein the transmitter is arranged for type burst 1 UTRA TDD data transmission.

- 9 The transmitter according to claim 6 or 7 wherein:

the transmitter further comprises means for applying to the midamble a third shift representative of a third signal indicative of whether the number of codes in the subset is odd or even.

The transmitter according to claim 9 wherein the system is arranged for type burst 1 UTRA TDD data transmission or type burst 2 UTRA TDD data transmission.

11 A receiver for use in a radio communication system for coding a midamble with one of a subset of a predetermined set of midamble shift positions, which subset of includes all active codes, the receiver comprising:

means for recovering from a received midamble a first signal indicative of the position in the predetermined set of the final code of the active set;

means for recovering from the received midamble a second signal indicative of the number of codes which are not in the active set; and means for determining from the recovered first signal and the recovered second signal the set of active codes.

12 The receiver according to claim 11 wherein the receiver is arranged for UTRA TDD data reception.

13 The receiver according to claim 12 wherein the receiver is arranged for type burst 1 UTRA TDD data reception.

14 The receiver according to claim 11 or 12 wherein:

11 - the receiver further comprises means for recovering from the received midamble a third signal indicative of whether the number of codes in the subset is odd or even, and the means for determining is arranged to determine the set of active codes from the recovered first signal, the recovered second signal and the < 1 < recovered third signal.

The receiver according to claim 14 wherein the receiver is arranged for type burst 1 UTRA TDD data reception or for type burst 2 UTRA TDD data reception.

16 A radio communication system for coding a midamble with one of a subset of a predetermined set of midamble shift positions substantially as hereinbefore described with reference to the accompanying drawings.

17 A transmitter for use in a radio communication system for coding a midamble with one of a subset of a predetermined set of midamble shift positions substantially as hereinbefore described with reference to the accompanying drawings.

18 A receiver for use in a radio communication system for coding a midamble with one of a subset of a predetermined set of midamble shift positions substantially as hereinbefore described with reference to the accompanying drawings.