Resource Allocation in OFDM Based Wireless Relay Networks ...

3.2 System Model
MU
MU
3 8
A 1 2 7
3 8
2 7
A 3 1 4 5
1 4 5
B 1
A 2
1 2 5
1 2 5
RS
3 6 8
3 6 8 B 2
4 6 7
4 6 7
B 3
Figure 3.3: System model for an OFMDA aided multi-user TWRN.
broadcasts the received signal after certain processing, for example power amplifying
and carrier permutation. The two users of the m-th user pair, denoted as A m and
B m , transmit simultaneously on the same carriers, for example the kth carrier in
MAP, 1 while the received signal will be sent back over the j-th sub-carrier in BCP.
Assigning which carrier to which user-pair, as well as the matching strategy (k, j)
will be optimized in this work.
Denote the channel coefficient from A m to RS as h m,k , the one from B m to RS
as g m,k , the one from RS to A m as ˜h m,j , and the one from RS to B m as ˜g m,j . 2 Then
the received signal at RS is
√
√
yk RS = p A m,k h m,kx A m,k + p B m,k g m,kx B m,k + wk RS , (3.1)
where x A m,k and xB m,k are the information symbols to be exchanged, pA m,k and pB m,k
are the corresponding powers over the k-th carrier, and w RS
k
Gaussian noise with variance σ 2 .
is the additive white
If the power allocated at RS over sub-carrier j is represented as p R j , then the
1 That is to say, A m1 and B m2 will not transmit on the same carrier during MAP.
2 By letting ˜h m,j = h m,j and ˜g m,j = g m,j , the scenario here reduces to the reciprocal channels.
48