Sphere Decoder
Decode input using a sphere decoder
Library
MIMO
Description
This block decodes the symbols sent over Nt antennas using the sphere
decoding algorithm.
Data Type
For information about the data types each block port supports, see the Supported Data Type table on this page. The output signal inherits the data type from the inputs.
Algorithm
This block implements the algorithm, inputs, and outputs described on the comm.SphereDecoder
System
object™ block reference page. The object properties correspond to the block parameters.
Parameters
- Signal constellation
Specify the number of points in the signal constellation to which the bits are mapped. This value must be a complex column vector. The length of the vector must be a power of two. The block uses the same constellation for each transmit antenna. The default setting is a QPSK constellation with an average power of 1.
- Bit mapping per constellation point
Specify the bit mapping that the block uses for each constellation point. This value must be a numerical matrix. he matrix size must be [ConstellationLength bitsPerSymbol], where ConstellationLength represents the length of the Signal constellation parameter value and bitsPerSymbol represents the number of bits that each symbol encodes. The default matrix size is [0 0; 0 1; 1 0; 1 1], which matches the default value of the Signal constellation property.
- Initial search radius
Specify the initial search radius for the decoding algorithm as
InfinityorZF solution.When you select
Infinity, the block sets the initial search radius to Inf. When you selectZF solution, the block 'sets the initial search radius to the zero-forcing solution. The zero-forcing solution is calculated by the pseudo-inverse of the input channel when decoding. Large constellations and/or antenna counts can benefit from the initial reduction in the search radius. In most cases, however, the extra computation of theZF Solutionwill not provide a benefit.
- Decision method
Specify the decoding decision method as
SoftorHard. When you selectSoftthe block outputs log-likelihood ratios (LLRs), or soft bits. When you select set toHard, the block converts the soft LLRs to bits. The hard decision output logical array follows the mapping of a0for a negative LLR and1for all other values.- Simulation using
Specify if the block simulates using
Code generationorInterpreted execution. The default isInterpreted execution.
Supported Data Type
| Port | Supported Data Types |
|---|---|
| Rx |
|
| cEst |
|
| Output |
|
Limitations
The output LLR values are not scaled by the noise variance. For coded links employing iterative coding (LDPC or turbo) or MIMO OFDM with Viterbi decoding, the output LLR values should be scaled by the channel state information to achieve better performance.
Algorithms
This block implements the algorithm, inputs, and outputs described on the Sphere Decoder System object reference page. The object properties correspond to the block parameters.