In this paper, we theoretically analyze the performance of a multiplexing and error control scheme for body area networks. In our previous work, we proposed a quality of service (QoS) control optimization method that achieves optimal QoS control by introducing a multiplexing scheme over the media access control (MAC) layer. This multiplexing scheme combines Weldon-based hybrid automatic repeat request (ARQ) with a decomposable error-correcting code. In this paper, we present a theoretical analysis of our proposed scheme as an extension of our previous work. In this proposed system, the decomposable code which has simpler structure is utilized. We then show that our proposed multiplexing layer can achieve optimal performance at E s /N 0 = 3, 5, and 6 dB in the additive white Gaussian noise (AWGN) channel and at E s /N 0 = 8, 11, and 14 dB in the Rayleigh fading channel by arbitrarily selecting parameters for the error-correcting code and hybrid ARQ. Then, we show that the proposed system obtains over 1.2 dB gain in the AWGN channel and over 4.2 dB gain in the Rayleigh fading channel than IEEE802.15.6 in the optional pattern.