Efficient multichannel filtering for CDMA modems
AssigneeInterDigital Technology Corporation
InventorRobert T. Regis
Life of this patent
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Abstract
An efficient, multichannel filter for CDMA modems permits multiple serial, digital bit streams to be filtered by digital signal processing techniques including sample weighting and summing functions. Each individual channel may have custom weighting coefficients or weighting coefficients common for all channels. If the weighting coefficients are by adapation, the same approach may be taken. The multichannel FIR filter is implemented with no multipliers and a reduction in the number of adders. To increase the speed of operation, the filter structure utilizes look-up tables storing the weighting coefficients. The invention can be embodied as either as a field programmable gate array or an application specific integrated circuit. The use of look-up tables saves significant chip resources.
Claims17
A multichannel, digital filter for code division multiple access telecommunication systems comprising:
- a plurality of filter inputs, each input comprising a channel;
- a filter output;
- first and second memories, each memory coupled to said plurality of filter inputs and each memory having an output;
- a first storage register having an input coupled to the output of said first memory and having an output;
- a first summer having a first input coupled to said first storage register and a second input coupled to the output of said second memory, said first summer having an output;
- and
- a second storage register coupled to said output of said first summer and having an output;
- wherein said output of said second storage register comprises said filter output.
A multichannel digital filter for CDMA telecommunication applications comprising:
- a plurality of filter inputs;
- a filter output;
- addressing means, responsive to said plurality of filter inputs for generating a plurality of memory addresses;
- a plurality of memories coupled to said addressing means having a plurality of memory locations, each location corresponding to a memory address;
- each memory representing an individual tap of said digital filter and each said location for storing a precomputed weighting coefficient representing partial product weighted sums of convolutions of said digital filter;
- a first storage register coupled to a first memory representing a first filter tap;
- a first summer coupled to said first storage register and a second memory and having an output;
- a second storage register coupled to said first summer representing a second filter tap;
- a second summer coupled to said second storage register and a third memory and having an output;
- a third storage register coupled to said second summer representing a third filter tap;
- and
- a third summer coupled to said third storage register and a fourth memory to provide said filter output.
A method for digitally filtering a plurality of independent signal channels for a code division multiple access telecommunication systems application including a plurality of filter inputs and a filter output comprising the steps of:
- precomputing intermediate dot products for said digital filter incorporating filter tap weight coefficients and individual channel weights;
- storing said precomputed intermediate products in a plurality of memory locations representing filter taps in said digital filter;
- recalling said intermediate products in a selective sequential manner to provide memory outputs;
- storing said memory outputs in a plurality of storage registers;
- adding the contents of said storage registers to provide a summation;
- outputting said summation as said filter output.
Dependencies are inferred from the claim text.