Jamming energy allocation in training-based multiple access systems

We consider the problem of jamming attack in a multiple access channel with training-based transmission. First, we derive upper and lower bounds on the maximum achievable ergodic sum-rate which explicitly shows the impact of jamming during both the training phase and the data transmission phase. Then, from the jammer's design perspective, we analytically find the optimal jamming energy allocation between the two phases that minimizes the derived bounds on the ergodic sum-rate. Numerical results demonstrate that the obtained optimal jamming design reduces the ergodic sum-rate of the legitimate users considerably in comparison to fixed power jamming.The work of X. Zhou was supported by the Australian Research Council's Discovery Projects funding scheme (Project No. DP110102548)

How much training is needed in fading multiple access channels?

We optimize the tradeoff between multiuser diversity and training overhead in a single antenna narrowband multiple access channel with a large number of users. A block fading model with independent Rayleigh gains is considered, in which training sequences are sent to the base station one at a time and the user estimated to be the strongest is scheduled to transmit. Considering a lower bound on the ergodic sum capacity with channel uncertainty under an average total power constraint, we optimize the proportion of time and power spent on training in each block. By analyzing the asymptotic behavior of the system as the block length grows large, we optimize the number of users considered for transmission in each block with respect to an approximate expression for the achievable rate, and find first order expressions for the resulting parameters