4.2.12 Physical channel mapping

25.2223GPPMultiplexing and channel coding (TDD)Release 17TS

4.2.12.1 Physical channel mapping for the 3.84 Mcps and 7.68Mcps options

The PhCH for both uplink and downlink is defined in [7]. The bits after physical channel mapping are denoted by , where p is the PhCH number corresponding to the sequence number 1 p P of this physical channel as detailed below, U_p is the number of bits in one radio frame for the respective PhCH, and P. P_max. The bits w_p,k are mapped to the PhCHs so that the bits for each PhCH are transmitted over the air in ascending order with respect to k.

The physical layer shall assign the physical channel sequence number p to the physical channels of the CCTrCH in the respective radio frame, treating each allocated timeslot in ascending order. If within a timeslot there are multiple physical channels they shall first be ordered in ascending order of the spreading factor (Q) and subsequently by channelisation code index (k), as shown in [9].

The mapping of the bits is performed like block interleaving, writing the bits into columns, but a PhCH with an odd number is filled in forward order, whereas a PhCH with an even number is filled in reverse order.

The mapping scheme, as described in the following subclause, shall be applied individually for each timeslot t used in the current frame. Therefore, the bits are assigned to the bits of the physical channels in each timeslot.

In uplink there are at most two codes allocated (P2). If there is only one code, the same mapping as for downlink is applied. Denote SF1 and SF2 the spreading factors used for code 1 and 2, respectively. For the number of consecutive bits to assign per code bs_k the following rule is applied:

if

SF1 >= SF2 then bs₁ = 1 ; bs₂ = SF1/SF2 ;

else

SF2 > SF1 then bs₁ = SF2/SF1; bs₂ = 1 ;

end if

In the downlink case bs_p is 1 for all physical channels.

4.2.12.1.1 Mapping scheme

Notation used in this subclause:

P _t: number of physical channels for timeslot t , P_t = 1..2 for uplink ; P_t = 1…16 for downlink for 1.28Mcps TDD and 3.84Mcps TDD, P_t = 1…32 for 7.68Mcps TDD

U_t,p: capacity in bits for the physical channel p in timeslot t

U_t.: total number of bits to be assigned for timeslot t

bs_p: number of consecutive bits to assign per code

for downlink all bs_p = 1

for uplink if SF1 >= SF2 then bs₁ = 1 ; bs₂ = SF1/SF2 ;

if SF2 > SF1 then bs₁ = SF2/SF1; bs₂ = 1 ;

fb_p: number of already written bits for each code

pos: intermediate calculation variable

for p=1 to P _t — reset number of already written bits for every physical channel

fb_p = 0

end for

p = 1 — start with PhCH #1

for k=1 to U_t.

do while (fb_p == U_t,p) — physical channel filled up already ?

p = (p mod P_t) + 1;

end do

if (p mod 2) == 0

pos = U_t,p – fb_p — reverse order

else

pos = fb_p + 1 — forward order

endif

w_t,p,pos = v_t,k — assignment

fb_p = fb_p + 1 — Increment number of already written bits

if (fb_p mod bs_p) == 0 — Conditional change to the next physical channel

p = (p mod P_t) + 1;

end if

end for

4.2.12.2 Physical channel mapping for the 1.28 Mcps option

The bit streams from the sub-frame segmentation unit are mapped onto code channels of time slots in sub-frames.

The bits after physical channel mapping are denoted by , where p is the PhCH number and Up is the number of bits in one sub-frame for the respective PhCH. The bits wpk are mapped to the PhCHs so that the bits for each PhCH are transmitted over the air in ascending order with respect to k.

The mapping of the bits y_t,n,1, y_t,n,2, y_{t,n,3, …,} y_t,n,Ut is performed like block interleaving, writing the bits into columns, but a PhCH with an odd number is filled in forward order, were as a PhCH with an even number is filled in reverse order.

The mapping scheme, as described in the following subclause, shall be applied individually for each timeslot t used in the current subframe. Therefore, the bits y_t,n,1, y_t,n,2, y_{t,n,3, …,} y_t,n,Ut are assigned to the bits of the physical channels in each timeslot.

In uplink there are at most two codes allocated (P2). If there is only one code, the same mapping as for downlink is applied. Denote SF1 and SF2 the spreading factors used for code 1 and 2, respectively. For the number of consecutive bits to assign per code bsk the following rule is applied:

if

SF1 >= SF2 then bs₁ = 1 ; bs₂ = SF1/SF2 ;

else

SF2 > SF1 then bs₁ = SF2/SF1; bs₂ = 1 ;

end if

In the downlink case bs_p is 1 for all physical channels.

4.2.12.2.1 Mapping scheme

Notation used in this subclause:

P _t: number of physical channels for timeslot t , P_t = 1..2 for uplink ; P_t = 1…16 for downlink

U_tp: capacity in bits for the physical channel p in timeslot t in the current sub-frame

U_t.: total number of bits to be assigned for timeslot t in the current sub-frame

n = index of the current sub-frame (1 or 2)

bs_p: number of consecutive bits to assign per code

for downlink all bs_p = 1

for uplink if SF1 >= SF2 then bs₁ = 1 ; bs₂ = SF1/SF2 ;

if SF2 > SF1 then bs₁ = SF2/SF1; bs₂ = 1 ;

fb_p: number of already written bits for each code

pos: intermediate calculation variable

for p=1 to P _t — reset number of already written bits for every physical channel

fb_p = 0

end for

p = 1 — start with PhCH #1

for k=1 to U_t.

do while (fb_p == U_t,p) — physical channel filled up already ?

p = (p mod P _t) + 1 ;

end do

if (p mod 2) == 0

pos = U_t,p – fb_p — reverse order

else

pos = fb_p + 1 — forward order

end if

w_tp,pos =y_t,n,k — assignment

fb_p = fb_p + 1 — Increment number of already written bits

If (fb_p mod bs_p) == 0 — Conditional change to the next physical channel

p = (p mod P t) + 1 ;

end if

end for