Increasing storage capacity in multilevel memory cells by means of communications and signal processing techniques

Multilevel and analogue memory cells have the capability of storing considerably more than one bit of information per cell. The number of levels the memory cells can store is limited by noise and bit error probability. The authors propose using error correction coding and digital modulation techniques used in communication systems to increase the storage capacity of multilevel and analogue memory cells. They evaluate these techniques and find that compared to the methods that do not use coded modulation techniques, typically, one extra bit per cell (i.e. effectively doubling the number of levels per cell) in storage capacity can be achieved. The techniques can also be applied to improve readout bit-error probability and provide unequal error protection for the bits to be stored. The latter technique is important for the efficient storage of digitised multimedia signals such as speech, audio, image and video signals. One- and two-dimensional coded modulation schemes as well as uncoded multilevel digital modulation schemes are presented in detail. Complexity and speed issues are also considered