5A.6 Midamble Allocation for Physical Channels

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

Midambles are part of the physical channel configuration which is performed by higher layers. Four different midamble allocation schemes exist:

– UE specific midamble allocation: A UE specific midamble for DL or UL is explicitly assigned by higher layers.

– Default midamble allocation: The midamble for DL or UL is allocated by layer 1 depending on the associated channelisation code.

– Common midamble allocation: The midamble for the DL is allocated by layer 1 depending on the number of channelisation codes currently being present in the DL time slot.

– Speical Default midamble allocation: The midamble for DL or UL is also allocated by layer 1 depending on the associated channelisation code while the association is different from default midamble allocation.

If a midamble is not explicitly assigned and the use of the common midamble allocation scheme is not signalled by higher layers, the midamble shall be allocated by layer 1, based on default or special default midamble allocation scheme. This default or special default midamble allocation scheme is given by a fixed association between midambles and channelisation codes, and shall be applied individually to all channelisation codes within one time slot. Different associations apply for different burst types and cell configurations with respect to the maximum number of midambles.

The associations between channelisation codes and midambles for the default, special default and common midamble allocation differ from the 3.84 Mcps TDD option. The associations are given in Annex AA.2 [Association between Midambles and channelisation Codes for default midamble allocation], Annex AA.3 [Association between Midambles and channelisation Codes for special default midamble allocation]] and BA [Signalling of the number of channelisation codes for the DL common midamble case for 1.28Mcps TDD] respectively.

However, for timeslots employing MBSFN operation there is no single midamble restriction per MBSFN timeslot, i.e. K_Cell≥1, whilst this does not undermine the specification that all physical channels in such timeslots employ the same midamble(s) and thus default and common midamble allocation amount to the same allocation strategies.

5A.6.1 Midamble Allocation for DL Physical Channels

Beacon channels shall always use the reserved midambles m⁽¹⁾ and m⁽²⁾, see 5A.5. For the other DL physical channels that are located in timeslot #0, midambles shall be allocated based on the default midamble allocation scheme, using the association for K=8 midambles. For all other DL physical channels, the midamble is explicitly assigned by higher layers or allocated by layer 1.

5A.6.1.1 Midamble Allocation by signalling from higher layers

The midamble allocation by signalling is the same like in the 3.84 Mcps TDD cf. [5.6.1.1 Midamble allocation by signalling from higher layers]

5A.6.1.2 Midamble Allocation by layer 1

5A.6.1.2.1 Default midamble

The default midamble allocation by layer 1 is the same like in the 3.84 Mcps TDD cf. [5.6.1.2.1 Default midamble]. The associations between midambles and channelisation codes are given in Annex AA.2 [Association between Midambles and channelisation Codes for default midamble allocation].

If the variable E_DCH_SPS_STATUS = TRUE then two E-HICHs associated with the same midamble shift in the same timeslot can be configured.

5A.6.1.2.2 Common Midamble

The common midamble allocation by layer 1 is the same like in the 3.84 Mcps TDD cf. [5.6.1.2.2 Common midamble]. The respective associations are given in Annex BA [Signalling of the number of channelisation codes for the DL common midamble case for 1.28 Mcps TDD].

5A.6.1.2.3 Special Default Midamble

For MIMO dual stream transmission, there are two patterns (pattern 1 and pattern 2) of the association between midambles and channelisation codes for special default midamble allocation scheme for each cell configurations with respect to the maximum number of midambles.

For MU-MIMO transmission, there are four patterns (pattern 1A, pattern 1B, pattern 2A and pattern 2B) of the association between midambles and channelisation codes for special default midamble allocation scheme for each cell configurations with respect to the maximum number of midambles.

If the UE is configured in MIMO or MU-MIMO mode and the default midamble allocation scheme is signalled to the UE by higher layers, the default or special default midamble allocation scheme can be used. Whether the default or special default midamble allocation scheme is used is signalled to the UE by the related physical channe in [7]. The association between midambles and channelisation codes for the special default midamble allocation scheme for both MIMO dual stream transmission and MU-MIMO transmission are given in Annex AA.3 [Association between Midambles and channelisation Codes for special default midamble allocation].

5A.6.2 Midamble Allocation for UL Physical Channels

The midamble allocation for UL Physical Channels is the same as in the 3.84 Mcps TDD cf. [5.6.2 Midamble allocation for UL Physical Channels]