Wideband TDMA digital cellular mobile radio schemes can offer a capacity similar to that of analogue modulation schemes. To find the optimum coding to be used a balance must be made between bandwidth, power and number of channels. A comparison is made for an idealised system using QPSK transmission and biorthogonal coding. Coding with a bandwidth expansion of 2.7 is shown to provide a good capacity at low carrier/noise ratio and an acceptable error rate.