Bit error rate (BER) is analyzed theoretically for diversity reception in the quasi-static Rayleigh fading environment with noise and co-channel interference conditions. The analysis is based upon the canonic receiver model with postdetection combining. This model presents exact BER formulas with respect to carrier-to-noise ratio (CNR) and carrier-to-interference ratio (CIR) for both coherent and differential detections (CD and DD) of binary angle modulations. In the case of CD, an exact and explicit BER formula for the maximal-ratio combining diversity (MRC) is obtained. On the other hand, in the case of DD, an explicit BER formula for the equal-gain combining diversity (EGC) is obtained. These results are applied to derive an approximate BER formula of M-ary (M = 4, 8, 16) angle modulations. Phase-shift keying (PSK) and continuous-phase frequency-shift keying (CP-FSK) are demonstrated as examples of angle modulations.