Abstract: Tile based interleaving and de-interleaving of row-column interleaved data is described. In one example, the de-interleaving is divided into two memory transfer stages, the first from an on-chip memory to a DRAM and the second from the DRAM to an on-chip memory. Each stage operates on part of a row-column interleaved block of data and re-orders the data items, such that the output of the second stage comprises de-interleaved data. In the first stage, data items are read from the on-chip memory according to a non-linear sequence of memory read addresses and written to the DRAM. In the second stage, data items are read from the DRAM according to bursts of linear address sequences which make efficient use of the DRAM interface and written back to on-chip memory according to a non-linear sequence of memory write addresses.

Abstract: Methods and apparatus for efficient demapping of constellations are described. In an embodiment, these methods may be implemented within a digital communications receiver, such as a Digital Terrestrial Television receiver. The method reduces the number of distance metric calculations which are required to calculate soft information in the demapper by locating the closest constellation point to the received symbol. This closest constellation point is identified based on a comparison of distance metrics which are calculated parallel to either the I- or Q-axis. The number of distance metric calculations may be reduced still further by identifying a local minimum constellation point for each bit in the received symbol and these constellation points are identified using a similar method to the closest constellation point. Where the system uses rotated constellations, the received symbol may be unrotated before any constellation points are identified.

Abstract: Noise variance estimation and interference detection is described. In one example, a method of estimating noise variance is described in which the pilots within a received OFDM signal are divided into bands and then a noise variance estimate is calculated on a per-band basis by averaging the noise estimates for those pilots within the band. In some examples, the pilots are divided into bands in frequency and in other examples, the pilots are divided into bands in frequency and time, such that noise estimates from more than one OFDM symbol are used in calculating the per-band noise variance estimates. The noise variance estimate for a pilot is then set to the noise variance estimate for the band which contains the pilot. The noise variance estimate for a data sub-carrier can then be determined by interpolating between the values for the pilots.