Increasing concurrent transmissions in CDMA ad hoc networks

In ad hoc networks successful transmission between two nodes are ensured by inhibiting transmitters around each receiver. The paper shows that this minimum separation (Critical Radius) can be reduced by employing spread spectrum (CDMA) at the physical layer. Analytical expressions of critical radius for different multiple access schemes are compared. The improvement in capacity at the cost of bandwidth expansion for an ad hoc network in which nodes are uniformly distributed is presented. This trade off is shown to make sense as the number of nodes increases. A system design is also developed for CDMA based ad hoc networks, combining CSMA and CDMA to provide universal spatial reuse and high robustness to packet collisions.