Air Interface
The air interface connects the BTS to mobile stations over RF per C.S0002-E.
| Mechanism | Details |
|---|
| PN Spreading | Short PN codes (I/Q, period 2^15), identifies BS via PN offset |
| Walsh Channelization | 64 orthogonal codes multiplex forward channels |
| Long Code | 42-bit LFSR (period 2^42 - 1), user separation on reverse link |
| Chip Rate | 1,228,800 cps (SR1) |
| Channel | Walsh | Purpose |
|---|
| Pilot | W0 | Timing reference, coherent demodulation |
| Sync | W32 | System time, PN offset |
| Paging | W1 | Overhead messages, pages, channel assignments |
| Traffic | Assigned | User voice/data, power control bits |
| F-SCH | Assigned | Supplemental data (not yet active) |
| Channel | Purpose |
|---|
| Access | Registration, origination, page response |
| Traffic | User voice/data frames |
| Reverse Pilot | Coherent reference for RC3 (gated) |
| RC1 | RC3 |
|---|
| Compatibility | IS-95A | CDMA2000 1x |
| Forward modulation | BPSK | QPSK |
| Coding | R=1/2, K=9 | R=1/4, K=9 |
| Data rates | 9600/4800/2400/1200 bps | 9600/4800/2700/1500 bps |
| Reverse modulation | 64-ary Walsh | BPSK + pilot |
| Reverse pilot | No | Yes (gated) |
| Per-PCG power control | No | Yes |
| Status | Done | Done |
| Step | Operation |
|---|
| 1 | CRC attachment |
| 2 | Tail bit insertion |
| 3 | Convolutional encoding (R=1/2 or R=1/4) |
| 4 | Symbol repetition (rate matching) |
| 5 | Block interleaving |
| 6 | Walsh spreading |
| 7 | PN spreading (I/Q) |
| 8 | Pulse shaping (matched FIR filter) |
The inverse chain, implemented as a pipelined processor — see Receiver Pipeline.
