In this work, different approaches for improving the bandwidth efficiency of Multiple Access Channels have been proposed. Such improvements can be achieved with methods that use network coding or with methods that implement successive decoding. Both of these two methods have been discussed here. Under the first method, two novel schemes for using network coding in cooperative networks have been proposed. In the first scheme, network coding generates some redundancy in addition to the redundancy that is generated by the channel code. In the second scheme, the relay by use of the network code,...