9 The EDGE multiplexing function

3GPP44.021Rate adaption on the Mobile Station - Base Station System (MS - BSS) interfaceTS

In EDGE configurations the number of channels across the radio interface and that of substreams do not necessarily match. In such cases a multiplexing function described below shall be used at MS and BTS (3GPP TS 48.020). These functions distribute data between the substreams and radio channels.

At the MS the multiplexing function multiplexes 14.5 kbit/s substreams  produced either by the combination of Split/Combine and RA1/RA1′ or RA1′ functions in the transparent case, or by the combination of Split/Combine and RLP functions in the non-transparent case  into the TCH/F28.8 or TCH/F43.2 EDGE radio interface channels.

In the case of transparent 56 kbit/s or 64 kbit/s operation, the multiplexing function maps the data stream into two EDGE TCH/F32.0 radio interface channels.

9.1 Data block distribution into the substreams by the Multiplexing function; TCH/F28.8 channel coding

The multiplexing function maps/extracts two 14.5 kbit/s substreams into/from a 29.0 kbit/s radio interface channel.

A radio interface data block for a TCH/F28.8 channel contains the bit sequence: M1, M2, 288 user data bits, M1, M2, and 288 user data bits, in other words, the block is a combination of two TCH/F14.4 radio interface data blocks. The two TCH/F14.4 blocks belong to two separate substreams. One 580-bit block is transmitted/received every 20 ms.

a) Transparent services

In uplink, the multiplexing function maps one 290-bit block from each substream into every 580-bit TCH/F28.8 radio interface data block. Blocks from one stream always occupy the same half of the 580-bit radio interface data blocks.

In downlink, the multiplexing function demultiplexes the two substreams by extracting the two 290-bit blocks from the received 580-bit radio interface blocks; the 290-bit blocks belonging to one substream are carried in the same half of the 580-bit radio interface blocks.

b) Non-transparent services

The multiplexing function works in the same way as in the transparent case, i.e. the multiplexing is based on the use of 290-bit blocks, which  in this case  contain halves of 576-bit RLP frames.

9.1.1 AIUR of 57.6 kbit/s; Radio interface rate of 2 × 29.0 kbit/s

Non-transparent 57.6 kbit/s radio interface user rate can be achieved by using a combination of two TCH/F28.8 channels across the radio interface. Two parallel multiplexing functions are applied; the operation of both of these is as described in section 9.1 above.

9.2 Data block distribution to the radio interface by the Multiplexing function; TCH/F32.0 channel coding

The multiplexing function divides the datastream into blocks of ten 64-bit V.110 frames (Figure 14) in case of the 56 kbit/s user rate or into blocks of 640 data bits in case of the 64 kbit/s user rate. These blocks are distributed cyclically into timeslots a (0a6) and a+n (1a+n7) in each TDMA-frame; in the data stream, data mapped into timeslot a precedes that mapped into slot a+n. The receiving Multiplexing function recombines overall data stream from radio-interface channels so that the data carried by timeslot a (0a6) precedes the data carried by timeslot a+n (1a+n7) of the same TDMA-frame.

9.2.1 AIUR of 56 kbit/s; Radio interface rate of 2 × 32.0 kbit/s

Two blocks of 10 64-bit V.110 frames (Figure 14) are sent/received every 20 ms over the radio interface.

No V.24 status or NIC-information is transferred in association with AIUR 56 kbit/s.

No substream numbering is needed as just one substream is used across a two–timeslot radio interface channel.

9.2.2 AIUR of 64 kbit/s; Radio interface rate of 2 × 32.0 kbit/s

Two blocks of 640 data bits are sent/received through the radio interface every 20 ms.

No V.24 status or NIC-information is transferred in association with AIUR 64 kbit/s.

No substream numbering is needed as just one substream is used across a two–timeslot radio interface channel.

9.3 Data block distribution into the substreams by the Multiplexing function; TCH/F43.2 channel coding

The multiplexing function maps/extracts three 14.5 kbit/s substreams into/from a 43.5 kbit/s radio interface channel.

A radio interface data block for a TCH/F43.2 channel is a combination of three TCH/F14.4 radio interface data blocks. The three TCH/F14.4 blocks belong to separate substreams. One 870-bit block is transmitted/received every 20 ms.

The TCH/F43.2 channel is used only in non-transparent operation. Therefore, the 290-bit blocks handled by the multiplexing function carry halves of 576-bit RLP frames.

In uplink, the multiplexing function maps one 290-bit block from each substream into every 870-bit TCH/F43.2 radio interface data block. Blocks from one stream always occupy the same third of the 870-bit radio interface data blocks.

In downlink, the multiplexing function demultiplexes the three substreams by extracting the 290-bit blocks from the received 870-bit radio interface blocks; the 290-bit blocks belonging to one substream are carried in the same third of the 870-bit radio interface blocks.