**5. Conclusion and future research directions**

Central Unit for precoding calculation

**Figure 9.** Example of Tidy Three Multi-cells Cooperation (Exchanging Both the Data and the CSI)

<sup>ϕ</sup><sup>1</sup> <sup>=</sup>ε*<sup>d</sup>* <sup>α</sup> where ε, *<sup>d</sup>* <sup>α</sup> are the intercept, BS to MS distance

Signal to noise ratio at the cell edge (2-20) dB

The number of simulation runs 1000 simulations running

and path loss exponent [72, 73].

26 Selected Topics in WiMAX

**Table 2.** System Simulation Parameters.

**Channel Parameter Parameter Value**

<sup>ϕ</sup><sup>2</sup> =10ξ/10 <sup>ξ</sup>is generated as zero mean real value Gaussian

System configuration notations *E* denotes the number of cooperated cells.

ε =1.35×10<sup>7</sup>

cells.

Figure 10. shows the simulated average user rate performance for the MU-MIMO MCP. In this figure, the proposed algorithm result is denoted by PA-SLNR-FK-MCP and the conventional precoding methods of PU-SLNR-GEVD-MCP and PU-SLNR-GSVD-MCP and as a benchmark

end user.

, α = −3

*B* denotes the number of user.

random variable with standard deviation equal to 8dB

*NT* denotes the number of transmit antennas at each

*N***R** denotes the number of receive antennas at each

To conclude, this chapter has introduced the principles of MIMO techniques, reviewed various MU-MIMO precoding methods, and extended the knowledge by proposing a new method that outperformed the methods available in the literature. The results as shown in in fig‐ ure10, demonstrated conclusively the significant role of precoding in inter-cell interference cancelation in MCP scenario. There are still some interesting open issues and topics for future research related to this application. For example related to the data and CSI sharing, basically we assume perfect system interconnection in TDD mode of operation but how much system pilot is needed for the multi-cell cooperation is an open problem. Also we assume that there is no system error or delay. This assumption is an ideal assumption for typical system deployment. The real conditions are non-ideal, therefore, modeling and investigation of the effects of system errors and delay are also an open issue that need to be researched.

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