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, Up is the number of bits in one radio frame for the respective PhCH, and P. Pmax. The bits wp,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 (P2). 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 bsp 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 , Pt = 1..2 for uplink ; Pt = 1…16 for downlink for 1.28Mcps TDD and 3.84Mcps TDD, Pt = 1…32 for 7.68Mcps TDD
Ut,p: capacity in bits for the physical channel p in timeslot t
Ut.: total number of bits to be assigned for timeslot t
bsp: number of consecutive bits to assign per code
for downlink all bsp = 1
for uplink if SF1 >= SF2 then bs1 = 1 ; bs2 = SF1/SF2 ;
if SF2 > SF1 then bs1 = SF2/SF1; bs2 = 1 ;
fbp: 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
fbp = 0
end for
p = 1 — start with PhCH #1
for k=1 to Ut.
do while (fbp == Ut,p) — physical channel filled up already ?
p = (p mod Pt) + 1;
end do
if (p mod 2) == 0
pos = Ut,p – fbp — reverse order
else
pos = fbp + 1 — forward order
endif
wt,p,pos = vt,k — assignment
fbp = fbp + 1 — Increment number of already written bits
if (fbp mod bsp) == 0 — Conditional change to the next physical channel
p = (p mod Pt) + 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 yt,n,1, yt,n,2, yt,n,3, …, yt,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 yt,n,1, yt,n,2, yt,n,3, …, yt,n,Ut are assigned to the bits of the physical channels in each timeslot.
In uplink there are at most two codes allocated (P2). 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 bsp 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 , Pt = 1..2 for uplink ; Pt = 1…16 for downlink
Utp: capacity in bits for the physical channel p in timeslot t in the current sub-frame
Ut.: 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)
bsp: number of consecutive bits to assign per code
for downlink all bsp = 1
for uplink if SF1 >= SF2 then bs1 = 1 ; bs2 = SF1/SF2 ;
if SF2 > SF1 then bs1 = SF2/SF1; bs2 = 1 ;
fbp: 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
fbp = 0
end for
p = 1 — start with PhCH #1
for k=1 to Ut.
do while (fbp == Ut,p) — physical channel filled up already ?
p = (p mod P t) + 1 ;
end do
if (p mod 2) == 0
pos = Ut,p – fbp — reverse order
else
pos = fbp + 1 — forward order
end if
wtp,pos =yt,n,k — assignment
fbp = fbp + 1 — Increment number of already written bits
If (fbp mod bsp) == 0 — Conditional change to the next physical channel
p = (p mod P t) + 1 ;
end if
end for