Digital cellular land mobile telecommunication systems

1.2 System configuration

2 Technical characteristics

2.1 Forward link

2.1.1 RF interface

2.1.1.1 Data modulation

2.1.1.2 Spreading modulation

The radiated waveform is tightly band-limited to a bandwidth of either 4.1, 8.2, or 12.3 MHz. Base stations are distinguished from one to another by the relative phases of their spreading sequences.

2.1.2 Channel structure

Hadamard codes are used to provide orthogonality for each channel, which enables the separation of 64, 128, or 192 channels at the personal station receiver.

2.1.2.1 Pilot channel

2.1.2.2 Sync channel

FIGURE 12 [1073-12]= 16.5 CM

2.1.2.3 Paging channels

2.1.2.4 Traffic channels

The traffic channels carry coded speech or other information. Data rates of 64, 32, and 16 kbit/s are available frame by frame on the traffic channel. The rate variation is achieved by the repetition of symbols with the energy per bit kept constant.

2.1.3 Coding and interleaving

The forward link is convolutionally coded and block interleaved. The coding is rate 1/2 with a constraint length of 9. The interleaving span is 5 ms on the sync and paging channels. The interleaving span on the traffic channel is 5 ms with options of 10 or 20 ms.

The sync and paging channel messages are protected by a 32-bit cyclic redundancy code (CRC), which can be used by the receiver to detect decoding failures.

2.1.4 Reverse link power control bit stream

The forward traffic channels are punctured at 2 kbit/s for independent closed loop power control of each personal station. Either 2 or 4, or 8 symbols per power control bit are used, respectively, at 64, 32 or 16 kbit/s traffic data rates. The power control bit stream is uncoded.

2.2 Reverse link

2.2.1 RF interface

2.2.1.1 Data modulation

Data modulation on the reverse link is coherent QPSK at a symbol rate of 64 ks/s.

2.2.1.2 Spreading modulation

BPSK spreading modulation is used for inphase (I) and quadrature phase (Q) channels by pseudorandom and Hadamard sequences with chip rates of 4.096, 8.192 or 12.288 Mchip/s and a period of 20 ms.

The radiated waveform is tightly band limited to a bandwidth of 4.1, 8.2, or 12.3 MHz. Base stations are distinguished from one another by the relative phases of their spreading sequences.

2.2.2 Channel structure

The reverse link is composed of pilot, access, traffic, and signalling channels. Channelization of the reverse link is accomplished by adding pseudorandom and Hadamard sequences. The pseudorandom and Hadamard sequences have the same chip rate.

Hadamard codes are used to provide orthogonality among the pilot, traffic and signalling channels of each personal station.

2.2.2.1 Pilot channel

The pilot channel is associated with the traffic channel of the personal station. The pilot channel is spread but unmodulated. It serves as a phase reference for coherent demodulation of the other channels. It is also used as a search target for acquisition of a new base station when the personal station moves from one coverage area to another.

2.2.2.2 Access channel

The access channel is used either to respond to the base station paging channels or to originate a call, or to perform a registration. The access channel data rate is 16 kbit/s.

2.2.2.3 Traffic channel

The traffic channel carries coded speech or other traffic. Data rates of 64, 32, and 16 kbit/s are available frame-by-frame on traffic channel. The rate variation is achieved by repetition of symbols.

2.2.2.4 Signalling channel

The signalling channel is associated with the traffic channel of the personal station. The signalling channel rate is either 4 or 4, or 2 kbit/s, respectively, for data rates of 64, 32, or 16 kbit/s.

2.2.3 Coding and interleaving

Convolutional coding on the reverse link is rate 1/2, constraint length 9. The traffic channel is interleaved with 5 ms or optionally either 10 or 20 ms. The signalling channel is block interleaved with 5 ms.

2.2.4 Forward link power control

The power transmitted by the personal station is regulated to be near the minimum required for adequate error rate performance. The radiated power is determined by the received base station power information via the signalling channel.

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