Wireless Network Design: Optimization Models and Solution ...

308 Hang Jin and Li Guo
uplink power densities received at the BTS from different MS are the same if they
use the same MCS. For example, for MCS 0 (4QAM ), the uplink power density is
targeted at -125dBm measured in 10.938 kHz (The bandwidth of one carrier), and
for MCS 3 (16AM ), the power density is targeted at -116dBm measured in 10.938
kHz. The desired power density levels for different MCS are different to ensure that
the received signal can have sufficient CINR for each MCS (Table 13.2).
According to WiMAX protocol, the uplink power control is done on a per MS
basis. That is, there is only a single power control for each MS. If MS has multiple
burst with different MCS, it is MS’s reasonability to maintain different power
densities among various bursts with different desired MCS. For example, let MS A
have two bursts, where burst 1 uses 4QAM , and burst 2 uses 16QAM . Then, MS A
needs to allocate its transmitter power in such a way that the power density for the
second burst is 6dB higher than that of burst 1.
13.3.3.3 Uplink Open Loop Power Control
Due to the multi-path or/and MS mobility, the path loss between BS and MS varies
with time. To maintain a desired constant received signal level at BS, the MS needs
to vary its output power to compensate the path loss changes. The uplink open loop
power control is done as follows:
• MS receives the systems parameters including the receive sensitivities, antenna
gain, BS transmitted power, at the network entry (the systems parameters will be
broadcast periodically by BS).
• MS detects the down link signal level (preamble power)
• From the detected downlink power, BS antenna gain, and BS transmitted power,
MS computes the path loss as: PL = PBS + BSantgain − Ppreamble where PBS
is the BS transmitted power, BSantgain is BS antenna gain, and Ppreamble is
the detected preamble power.
• MS then computes the required transmitted power Ptx = Prx + PMCS + PL −
BSantgain where Prx is the required BS sensitivity, PMCS is the power offset
for the desired MCS, (it is the additional CINR required for this MCS beyond
that lowest MCS (4QAM )). Ptx is the current MS output power.
The open loop power control is done at MS side, and is transparent to BS.
Uplink Close Loop Power Control
Open loop power control can eliminate most of the signal variation due to the channel
fading and MS movement. However, the open loop power control varies the MS
transmitted power based on the down link signal variation, it does not factor in any
uplink signal degradation due to the uplink interferences or other impairments. To
rectify the issue, closed loop power control is added to help tune the uplink transmitted
power. As the name implies, closed loop power control requires commands