Frame level control for collision mitigation in orthogonal code hopping multiplexing

We have recently proposed an orthogonal code hopping multiplexing (OCHM) scheme which is based on a statistical multiplexing scheme for orthogonal downlink in direct sequence spread spectrum systems. This is a feasible candidate for accommodating a large number of bursty packet-based users with good backward compatibility. In OCHM, code-collisions which degrade channel coding performance and result in an increase in the required E_b/N₀ are inevitable for obtaining a statistical multiplexing gain. In this paper, we lower code-collision probability by discarding or delaying excessive frames whose number is larger than a threshold value. It reduces the required E_b/N₀ at the transmitter and saves system power. However, there is an increase in BLER (block error rate) or delay. Therefore, there exist trade-offs between the required E_b/N₀ and BLER (or delay). We can determine an operating point which can reduce the required E_b/N₀ by considering how much BLER or delay the system requires as a target value.