Analysis of a MIMO-OFDM Wireless Communication System Using a Binary Power Control Scheme with Radio Channel Uncertainties

Veiw figure View Figure

Each of the signal travelling form transmitting antenna undergoes several radio channel uncertainties like path loss, shadowing coefficient, multipath fading coefficient, and interference from other users. Assuming all these parameters the received signal is given by ^[13]

(1)

For first tier mobile unit it is given by

(2)

For second tier mobile unit it is given by

(3)

Where R is the distance between base station and user i, z is the Rayleigh fading coefficient, w is lognormal coefficient, and is the path loss coefficient.

Energy efficiency optimization is carried out by defining energy efficiency which is the ratio of channel capacity to the total power transmission with reference to Shannon capacity limit

(4)

(5)

Where S_i is the received signal and n_o is the AWGN in wireless sub-channel.

Here BPSK modulation scheme to investigate BER performance is adopted and is given by ^[13]

(6)

3. Binary Power Control Scheme

Binary power control is a power control scheme with only two allowable power values, usually 0 or P_max. Hence, a link can either transmit at a full power or be switched off completely. Binary power control (BPC) has the advantage of leading towards simpler or even distributed power control algorithms. Moreover, the binary power control scheme is formulated as ^[14]

(7)

Assuming this scheme, the number of subchannels are divided into two subsets one with minimum transmission power (MP_min) and other with maximum transmission power (MP_max). However, total number of channels used are N and subchannels are grouped into M. The wireless subchannel with maximum power is given by ^[13]

(8)

And, energy efficiency is as given in ^[13],

(9)

4. Performance Analysis

Based on the above discussed constraints i.e. firstly the subchannels are ordered digressively according to channel state information (CSI). Then the subchannels will either be allocated with Pmax or Pmin. After this the process of determining BER is carried out. This average bit error rate is compared with the threshold value (b) to guarantee the QoS. Typical values of radio channel uncertainties are listed in Table 1.

Table 1. Different parameters considered in EEBPCB algorithm

Download as

View current table in a new window

Tables index

Veiw figure View Table

From Figure 2 it is observed that for increase in number of subchannels in EEBPCB, the energy efficiency gets increased in comparison with average power control algorithm presented in ^[15].

Figure 3 shows the energy efficiency comparison of EEBPCB algorithm and average power control algorithm ^[16] as a function of total transmitted power. Here, as the signal power increases, the energy efficiency of MIMO-OFDM system goes on reducing. However, EEBPCB algorithm shows high efficiency for different power ratings in comparison with average power control algorithm ^[16].

Figure 2. Energy efficiency comparison for EEBPCB and average power control algorithm for different no of subchannels

Download as

Veiw figure View Figure

Figure 3. Energy efficiency comparison for EEBPCB and average power control algorithm with different transmitted power

Download as

Veiw figure View Figure

In another effort, bit error rate comparison of EEBPCB and EBPCB ^[13] as a function of different path loss coefficients is presented in Figure 4. However, for both the schemes the bit error rate is ascending with path loss coefficients. In case of EEBPCB algorithm there is a marginal loss in average bit error rate as compared with EBPCB.

Figure 4. Bit error rate comparison of EEBPCB and EBPCB as a function of different path loss coefficients

Download as

Veiw figure View Figure

Figure 5. Bit error rate comparison of EEBPCB and EBPCB with distance form base station

Download as

Veiw figure View Figure