wireless ad hoc networking

Supporting Multimedia Communication 619
mobiles/cell). However, the interference caused by the handoff mobiles I h
needs to be considered as a separate source from the general other-cellinterference
term, since they might transmit stronger signals than expected
(as shown in Section 23.4).
The received signal strength is modeled by a path loss model:
p j,i = P j r −µ
j,i 10 η 10 , where P j is the mobile’s transmitting power, r j,i the distance
between the mobile and base stations, µ (= 3.5) the path loss order,
and η the zero-mean random power fluctuation. We also assume that the
nonhandoff mobile is under perfect power control of its resident cell, with
a normalized received power level of 1 † .
Using the diversity decoding for uplink channel, the best link among
the active set is chosen for the jth handoff mobile. If A j is the active set of
the jth mobile, we have
SIR j = min
i∈A j
SIR j,i (23.14)
The SIR for the in-cell mobiles in each active set could be similarly obtained.
Note that the interference from all of the handoff mobiles is now regarded
as noise, and the regular in-cell mobile users have unit received signal
strength. For traffic type t in the ith active cell with spreading factor SF t ,
the SIR is approximated by
SIR(i, t) =
SF t
(m i + ∑ j (P jr −µ
j,i 10 η 10 ) + fI o )
(23.15)
Let H denote the set of handoff mobiles at any time. The optimal SF/power
assignments that maximum throughput for the handoff mobile can be
obtained by solving the following problem:
max z = ∑ j∈H
W
SF j
(23.16)
SIR j ≥ b j , j ∈ H (23.17)
SIR i,t ≥ b t , i ∈ A, and t ∈{traffic type set} (23.18)
23.4.4.3 Suboptimal SF/POWER Admission Algorithms
Without nonnegative power constraints, the optimal solution for Eq. (23.18)
can be obtained by Lagrange’s method after relaxing the SINR constraints
into linear form (see Ref. [7] for details). However, it might not result in
a feasible solution for the original problem due to the possible zero-value
† In practice, the received powers of different traffic are not uniformly assigned, thus
they cause a different level of interference.