Imbalances from imperfect phase modulators can cause distorted signal constellations and interfering tone signals at the carrier frequency in phase-modulated communication systems. The rendered imperfection in the modulated signal inevitably degrades the receiver’s carrier-tracking performance and, for quadraturephase-shift-keyed (QPSK) systems in particular, causes cross-talk between the inpha...

The frequency hopping (FH) based ultra-wideband (UWB) communication system divides its available frequency spectrum into several sub-bands, which leads to inherent disparities between carrier frequencies of each sub-band. Since the propagation loss is proportional to the square of the transmission frequency, the propagation loss on the sub-band having the highest carrier frequency is much large...

Multicarrier spread spectrum (MC-SS) systems exhibit good robustness against all kinds of narrowband interference, coloured noise or selective attenuation for power line communications. However, the systems’ vulnerability to frequency synchronization errors, which introduce loss of orthogonality between the subcarriers, is still a challenging problem for robust communications. This paper presen...

For integers n and k, the density Hales-Jewett number cn,k is defined as the maximal size of a subset of [k] that contains no combinatorial line. We prove a lower bound on cn,k, similar to the lower bound in [16], but with better dependency on k. The bound in [16] is roughly cn,k/k n ≥ exp(−O(log n)2 ) and we show cn,k/k n ≥ exp(−O(log n)). The proof of the bound uses the well-known constructio...