5A.2.3 Training sequences for spread bursts

25.2213GPPPhysical channels and mapping of transport channels onto physical channels (TDD)Release 17TS

In this subclause, the training sequences for usage as midambles are defined. The training sequences, i.e. midambles, of different users active in the same cell and same time slot are cyclically shifted versions of one single basic midamble code. In the case of MBSFN timeslots there is only a single midamble and this is derived from a single basic midamble code which is not necessarily cell-specific. The applicable basic midamble codes are given in Annex AA.1.

The basic midamble codes in Annex AA.1 are listed in hexadecimal notation. The binary form of the basic midamble code shall be derived according to table 8I below.

Table 8I: Mapping of 4 binary elements on a single hexadecimal digit:

4 binary elements	Mapped on hexadecimal digit
-1 -1 -1 -1	0
-1 -1 -1 1	1
-1 -1 1 –1	2
-1 -1 1 1	3
-1 1 -1 –1	4
-1 1 -1 1	5
-1 1 1 –1	6
-1 1 1 1	7
1 -1 -1 –1	8
1 -1 -1 1	9
1 -1 1 –1	A
1 -1 1 1	B
1 1 -1 –1	C
1 1 -1 1	D
1 1 1 –1	E
1 1 1 1	F

For each particular basic midamble code, its binary representation can be written as a vector:

(1)

According to Annex AA.1, the size of this vector is P=128. As QPSK modulation is used, the training sequences are transformed into a complex form, denoted as the complex vector:

(2)

The elements of are derived from elements of using equation (3):

for all (3)

Hence, the elements of the complex basic midamble code are alternating real and imaginary.

To derive the required training sequences, this vector is periodically extended to the size:

(4)

Notes on equation (4):

K and W are taken from Annex AA.1

So we obtain a new vector containing the periodic basic midamble sequence:

(5)

The first P elements of this vector are the same ones as in vector , the following elements repeat the beginning:

for the subset (6)

Using this periodic basic midamble sequence for each user k a midamble of length L_m is derived, which can be written as a user specific vector:

(7)

The L_m midamble elements are generated for each midamble of the k users (k = 1,…,K) based on:

with and (8)

The midamble sequences derived according to equations (7) to (8) have complex values and are not subject to channelisation or scrambling process, i.e. the elements represent complex chips for usage in the pulse shaping process at modulation.

The term ‘a midamble code set’ or ‘a midamble code family’ denotes K specific midamble codes ; k=1,…,K, based on a single basic midamble code according to (1).