RACH Channel Multiplexing - 2.0 English

RFSoC DFE PRACH LogiCORE IP Product Guide (PG391)

Document ID
PG391
Release Date
2024-05-30
Version
2.0 English

The data output channel from the DFE PRACH core makes use of the AXI4 TID signal to identify the RACH channel and antenna to which each output sample belongs. In general, the sequence of channels and antennas is highly variable because of the low data rate per channel and the sporadic nature of PRACH opportunities within the radio frame structure.

Two examples of PRACH data output are shown below. The following diagram illustrates an example system with two antennas.

Figure 1. System with Two Antennas

In this diagram, three PRACH captures are in progress. The data samples are written as Rr,a(s) where r is the RACH channel identifier (RCID), a is the antenna number and s is the sample index. The value of r is output on bits [3:0] of TID and the value of a is output on bits [7:4]. Samples belonging to the same channel are shown in the same color. Note that the sample index itself is not output by the core.

Because each RACH channel in this example is using a different sample rate and schedule, there is no overall pattern in the position of the output samples. Channels and antennas may be interleaved arbitrarily and the sample stream will be aperiodic. The only guaranteed behavior is that the samples of each RACH channel will always emerge in linear order (from earliest in time to latest in time).

The following diagram illustrates a system with eight antennas. In the eight antenna case, the number of output lanes is forced to be two, therefore in the diagram, TDATA is 64 bits wide. If the number of output lanes is two, the "odd" antenna samples appear on bits [63:32] of TDATA and the "even" antenna samples appear on bits [31:0].

Figure 2. System with Eight Antennas

Two ongoing PRACH captures are shown. In this diagram there are two output lanes, because the number of antennas is greater than four.

The two data samples output in parallel on a given clock cycle always belong to the same RACH channel. The value output on TID bits [7:4] in this case indicates which pair of antennas the samples belong to. A value of 0 means the samples belong to antennas 0 and 1; a value of 1 means they belong to antennas 2 and 3, and so on. As in the previous example, the interleaving of channels and antennas is arbitrary.

The decoding of the output TID field and the corresponding position of data on the output bus is shown in the following table.

Table 1. TID Field
Number of PRACH Output Lanes TID[3:0] TID[7:4] TDATA[31:0] TDATA[63:32]
1 RCID number (0-15) Antenna number

a (0-3)

Sample for antenna a N/A
2 RCID number (0-15) Antenna pair number

p (0-3)

Sample for antenna 2p Sample for antenna 2p+1