|Publication number||USRE41025 E1|
|Application number||US 11/139,004|
|Publication date||Dec 1, 2009|
|Filing date||May 26, 2005|
|Priority date||May 15, 1998|
|Also published as||DE69832589D1, DE69832589T2, EP0957604A1, EP0957604B1, US6570889|
|Publication number||11139004, 139004, US RE41025 E1, US RE41025E1, US-E1-RE41025, USRE41025 E1, USRE41025E1|
|Inventors||Richard Stirling-Gallacher, Jens-Uwe Jurgensen|
|Original Assignee||Sony Deutschland Gmbh|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (17), Non-Patent Citations (1), Classifications (18), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates to a transmitter, a wireless transmission system as well as to a method for the transmission of data symbols over a communication channel which particularly finds its application in the field of so-called CDMA systems.
CDMA (Code Division Multiple Access) transmitting systems are known from the state of the art. According to one CDMA technique, after the modulation (symbol mapping), the symbols are spread by a so-called spreading sequence or spreading code. After spreading the resulting data stream is scrambled by a scrambling sequence of a scrambling code. The thus resulting data stream, which has been spread and scrambled, is then power-amplified and sent over a communication channel. The reverse procedure happens at the receiving side.
From WO96/05668 A1 and EP-A-565 506 techniques for multiple access coding for radio communication is known. According to these documents information symbols are spread using orthogonal or bi-orthogonal codewords. This spread information symbols are assigned a unique scramble mask that is taken from a set of scramble masks having selected correlation properties. The set of scramble masks is selected such that the correlation between the modulo-2 sum of two scramble masks with any codeword is a constant magnitude independent of the codeword and the individual mask being compared. According to one embodiment of WO 96/05668 A1, when any two masks are summed using modulo-2 sum arithmetic, the Walsh transformation of that sum results in a maximally flat Walsh spectrum. For cellular radio telephone systems using subtractive CDMA demodulation techniques, a two-tier ciphering system ensures security at the cellular system level by using a pseudorandomly generated code key to select one of the scramble masks common to all of the mobile stations in a particular cell. As according to these techniques one common scramble mask is used for all mobile stations in a particular cell, the above-cited drawback arises that only certain types of channelisation codes can be used together limiting the number of available channelisation (spreading) codes.
In view of the above-cited drawbacks it is of the object of the present invention to enhance the flexibility of code assignment for a CDMA system, particularly within a cell sector and/or to increase the maximum data rate.
The central idea of the present invention thereby is a new code allocation scheme for a CDMA system utilising two or more scrambling codes within one link (uplink or downlink).
According to the present invention therefore a transmitter for communicating data symbols over a communication channel is provided, the transmitter comprising means for spreading each data symbol with a respective spreading code, wherein the spreading codes are mutually orthogonal. Furthermore means for scrambling each spread symbol with a respective scrambling code are provided, the scrambling codes respectively having the same length as the spreading codes. Means are provided for the transmission of the spread and scrambled symbols. According to the present invention the means for scrambling are provided with a plurality of different scrambling codes which can be used simultaneously within the same link.
The means for scrambling the spread symbols can use different scrambling codes for an uplink communication channel and a downlink communication channel.
The spreading codes can be obtained by means of a code tree.
According to an aspect of the present invention, only in a downlink communication channel different scrambling codes are used, wherein in an uplink channel only one scrambling code is used.
The means for scrambling can use different scrambling codes within the same link only for channels demanding a high bit rate.
According to the present invention, furthermore a wireless transmission system comprising a transmitter of the above-cited type is provided, wherein a subset of scrambling codes is respectively allocated to a cell of the transmission system.
Different spreading codes can be allocated to adjacent cells of the transmission system.
According to the present invention, furthermore a method for the transmission of data symbols over a communication channel is provided. Data symbols are spread with a respective spreading code, wherein the respective spreading codes are mutually orthogonal. Each spread symbol is scrambled with a respective scrambling code, the scrambling codes not changing the band rate of the transmission (in contrast to the spreading codes). The spread and scrambled symbols are transmitted.
According to the present invention, when scrambling a plurality of different scrambling codes can be used, which are to be used simultaneously within the same link.
In the step of scrambling different scrambling codes can be used for an uplink communication channel and a downlink communication channel, respectively.
The spreading codes can be obtained by means of a code tree.
As an aspect of the present invention, only in a downlink communication channel different scrambling codes are used. In the uplink communication channel only one scrambling code is used, as the bit rate usually is less than in the downlink communication channel.
Different scrambling codes can be used within the same link only for channels demanding a high bit rate.
Particularly different scrambling codes within the same link can be used for example for video channels and/or data channels, but for example not for voice channels.
Further aspects, advantages and features of the present invention will now be explained by means of embodiments of the present invention and with reference to the enclosed figures of the drawings.
A transmission system according to the present invention will now be explained generally with reference to FIG. 1. As shown in
With reference to
For the uplink 27, according to the present invention either the same scrambling codes Cscramble 1, . . . , Cscramble M as in the case of the downlink 26, or another group of scrambling codes Cscramble 1′, . . . , Cscramble M′ or, as generally the uplink channel 27 demands for the same high bit rate as the downlink channel 26, even just one scrambling code can be used.
As it has already been set forth above, the downlink channel 26 or the uplink channel 27 can comprise subchannels for video and/or voice transmission. As one aspect of the present invention, different scrambling codes can be allocated for the scrambling of the channels demanding for a high bit rate, as it is the case, for example, for the transmission of video data. For transmission of, for example, voice data, only one scrambling code can be used.
Regarding the details of the spreading and scrambling process, particularly the modulo-2 sum operation for the scrambling at the transmission side and the multiplying operation for the descrambling at the reception side, the above-cited documents WO 96/05668 A1 and EP-A-565 506 are incorporated by reference. Particularly
According to the present invention the spreading codes are generated by a code tree. This technique is known from Adachi, “Tree-structured generation of orthogonal spreading codes with different lengths for forward link of DS-CDMA mobile radio”, Electronic Letters, January 1997, Vol. 33, No. 1, page 27, 28, which is incorporated herewith by reference.
Orthogonal spreading codes with different lengths can be generated by a tree-structure for orthogonal multiplexing of forward-link code-channels of different data rates in direct sequence code division multiple access DS-CDMA mobile radio. Thereby codes of the same layer of the tree constitute a set of Walsh functions and are orthogonal. Furthermore, any two codes of different layers of the tree structure are also orthogonal except for the case that one of the two codes is a mother code of the other.
As it has already been set forth in the introductory portion, when only one scrambling code (or long code) is used per link, there are restrictions of the combinations of codes which can be used for the orthogonal codes (see Adachi et al.) These restrictions may prevent a user from being allocated to a certain channel. These restrictions are especially important for high data rate users. Furthermore the highest data rate is restricted to the shortest orthogonal code.
As according to the present invention, two or more scrambling codes are assigned to one link (one user), the following advantages are achieved:
By only using two scrambling codes (M=2) per link (user), the total number of available channelisation codes (spreading codes) can be doubled and the maximum data rate can also be doubled.
As it has already been set forth above, according to the present invention one scrambling code is used in conjunction with a set of channelisation codes (spreading codes) depending upon the required data rate and services required. Adjacent base stations can use different scrambling codes and every base station uses a set of scrambling codes to maintain different links in each cell.
An application of the present invention will now be explained with reference to FIG. 5. According to the state of the art, if a new user requests, for example, a 2 Mbit/s service, the base station 24 is forced to allocate a new scrambling code (and code tree) to support this service. The codes in the code tree are therefore not optimally utilised.
To increase the flexibility of code assignment and increase the usage of the codes and the code tree, it is proposed to use as an option more than one scrambling code per link.
If, however, the new user 32 uses 2 (SF=4) orthogonal codes from scrambling code 1 and 1 (SF=4) orthogonal code from scrambling code 2, a 2 Mbit/s service can be supported and the codes and the code tree can be more optimally utilised.
By utilizing the scheme as shown in
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|U.S. Classification||370/479, 375/146, 455/450, 370/208|
|International Classification||H04J13/00, H04B1/707, H04L25/03, H04J11/00, H04B7/26, H04B7/24|
|Cooperative Classification||H04B1/707, H04J13/004, H04B7/2628, H04L25/03866|
|European Classification||H04B1/707, H04J13/00B7, H04L25/03E3, H04B7/26S|
|Nov 19, 2010||FPAY||Fee payment|
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