Transmitter, receiver and method in a telecommunication...

Details Transmitter, receiver and method in a telecommunication... Transmitter, receiver and method in a telecommunication...

1999-08-25

2003-04-29

Chin, Stephen (Department: 2734)

Pulse or digital communications

Spread spectrum

Direct sequence

C375S147000, C327S164000, C370S280000, C370S345000, C708S250000, C341S173000

Reexamination Certificate

active

06556618

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a transmitter, a receiver and a method in a telecommunication system for providing PN sequences for different user channels. In particular, the present invention relates to such a transmitter, receiver and method in a telecommunication system, in which a plurality of user channels are processed using a time-slot multiplexing of user data in respective transmission frames.
Such PN sequences are generally used for performing bit error rate measurements in telecommunication systems. For this purpose, a known PN sequence of a predetermined length, i.e. a predetermined number of bits 2
N
−1 (where N denotes the number of shift registers of the PN generator) is encoded in the transmitter and the received sequence is decoded in the receiver.
FIG. 1
shows a general overview of a typical decoder circuit in a CDMA-system, where the block “BER measurement {circle around (3)} ”evaluates the bit error rate BER by decoding a received PN-sequence (PN: Pseudo noise).
FIG. 2
shows the principle of performing such bit error rate measurement. A telecommunication system TELE comprises a transmitter TX and a receiver RX. In the transmitter TX a transmitter PN-generator T-PN (consisting of interconnected shift registers) is initialized with a predetermined sequence “111111111” and likewise at the receiver RX a PN-generator R-PN must be initialized with the same initializing sequence. It is essential, that the PN-generator T-PN in the transmitter TX and the PN-generator in the receiver RX are synchronized. As indicated in
FIG. 2
, one possibility is to use a control channel for setting the start timing of the PN-generators in the transmitter TX and in the receiver RX. Once the PN-generators have been initialized and started in the synchronized manner, the bit error rate measurement circuit in the receiver RX can compare the PN-sequence generated in the receiver with the received and decoded sequence from the transmitter TX in order to evaluate the discrepancies of the generated bits.
With respect to the PN-generators T-PN, R-PN, it may be noted that these PN-generators are generally constituted by a series connection of shift registers SH
1
-SHN with intermediate EXOR gates EX
1
-EXN−1 (where EX
1
denotes the first XOR gate and EXN−1 denotes the (N−1)th XOR gate, i.e. the last provided XOR gate) from which the input of the first shift register SH
1
of the PN-generator is built. This is a generally known configuration and an illustration of the general interconnection of the EXOR gates and the shift registers can be seen in FIG.
4
. That is, the actual length 2
N
−1 of the PN-sequence is determined by the number N of shift registers and the actual polynomial used for generating the PN sequence, i.e. the type of the PN-sequence is determined by the number of inputs to the EXOR gates for the first shift register, as is well-known.
Thus, both transmitter and receiver PN-generators T-PN, R-PN of the telecommunication system TELE in
FIG. 2
comprise such an interconnection of gates and shift registers and whenever user data of the user channel is to be coded by using the PN-sequence in a transmitter and using the PN-sequence in the receiver, the shift registers must be set with a predetermined sequence in a synchronized manner (where the bit sequence must not be a state of “all 0”).
BACKGROUND OF THE INVENTION
Whilst the general technique of performing bit error rate measurements using known PN-sequences and the constitution of the PN-generators as explained above is well-known in the prior art in order to evaluate one channel for one user, there are specific problems when time-slotted transmissions, i.e. time-slot multiplexing of user data on a plurality of user channels in respective transmission frames are used for the transmission between the transmitter TX and the receiver RX and/or for the processing of a plurality of user channels.
That is,
FIG. 2
only shows the situation for performing bit error rate measurements for one user channel and if there are a plurality of users (user channels) which use one frame in a time-slotted manner, then invariably several PN-generators must be used, each dedicated to one user channel. That is, assuming that in a telecommunication system, where communications and/or processings are carried out using such a time-slot multiplexing technique, for example up to 512 user channels (depending on the channel size) can be handled and thus 512 individual channel bit error rate measurements must be performed by respectively using their specifically dedicated PN-sequences.
In this connection, it should be noted that the expression “time-slot multiplexing of user data on a plurality of user channels in respective transmission frames” can relate to various different modulation schemes used in common telecommunication systems, i.e. TDMA multiplexing schemes or CDMA multiplexing schemes. The essential feature that is common to all such modulation schemes is that each user channel will be assigned a particular time-slot in a transmission frame. For example,
FIG. 1
shows the general overview over a CDMA system, where a number of user channels are input to a slot demultiplexer and a decoding is carried out in the time-slot segmentation, the bit interleaving and the Viterbi decoder, before the user data undergoes the bit error rate measurement in the block {circle around (3)}. Here, in this CDMA system, for example up to 512 user channels are received in individual bursts in associated time-slots of a transmission frame.
In
FIG. 3
two transmission frames FR of a time-slot mulitplexing system are shown. In each frame FR a great plurality of user channels (e.g. 512 user channels) must be accommodated. The complete user data of one user channel is distributed over a number of consecutive frames FR respectively at the same position (here at the beginning of the frame). However, the user data may also be distributed at different positions within the frame FR.
In
FIG. 3
the user channel of user
1
is allocated to the first time-slot position in the frame FR. Typically with a frame length of 10 ms, a slot of 1/512 of the frame and a bit period of 8 MHz, only about 100 bits of the complete PN-sequence generated by the transmitter or receiver PN-generator can be accommodated in the first time-slot (user channel) in the first frame FR, as illustrated in FIG.
3
. Of course, assuming for example N=9 shift registers in the PN-generator, the actual length of the Pseudo Noise sequence is 2
N
−1=511 bits. Therefore, of course only 100 bits are not sufficient in order to fully evaluate the channel for the user
1
. Therefore, assuming that the PN-generators in the transmitter and in the receiver were synchronized at the beginning of the first frame, then the bit error rate measurement can not be continuously performed for the user
1
, since only after a certain number of bits, i.e. 100 bits, the transmission is interrupted—for that user—within each frame. That is, after the first 100 bits of the first user channel
1
, the next 100 bits of user channel
2
are transmitted, that is, the other positions in the first frame FR are respectively allocated to the other users. Therefore, between the start timing and the end timing of each time-slot only a limited number of bits from the PN-sequence used for the user channel
1
can be evaluated.
The consequence of this is that the PN-generators must stop their operation—for the first user—at the end timing of each time-slot at the receiver and the transmitter and must continue their PN-sequence generation from the last state (i.e. from a last phase state of the PN-generators) at the start timing of the respective time slot in the next frame (i.e. in
FIG. 3
in the second frame FR). In particular, it is not possible to just let the PN-generator continue to output the bits of the bit sequence, when the next user channel starts, since the phase state, which the PN-generator had at the end timing of the first user time-slot, must be available, wh

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