Application-Specific Accelerators for Communications - Signal Processing Systems - page 740

Channel Matrix Received Vector

Pre-Processing Unit
(PPU)

Sphere
Detector

PD Unit
#1

Previous PD PD_1

Node Ordering Unit
(NOU )

PD Unit
#2
.

PD_2

Tree Traversal
Unit (TTU)

.

.

Computation Unit
(CMPU)

PD Unit
#w

PD _w

Computation Unit
(CMPU)

Detected Vector

Fig. 9 Sphere Detector architecture with multiple PED function units

2.2.4 Depth-First Sphere Detector Architecture

The depth-first sphere detection algorithm [ 12 , 19 , 25 , 31 ] traverses the tree in a
depth-first manner: the detector visits the children of each node before visiting its
siblings. A constraint, referred to as radius, is often set on the PED for each level
of the tree. A generic depth-first sphere detector architecture is shown in Fig. 9 .
The Pre-Processing Unit (PPU) is used to compute the QR decomposition of the
channel matrix as well as calculate Q H y . The Tree Traversal Unit (TTU) is the
controlling unit which decides in which direction and with which node to continue.
Computation Unit (CMPU) computes the partial distances, based on ( 4 ) , for w
different s j . Each PD unit computes

2 for each of the w children
of a node. Finally, the Node Ordering Unit (NOU) is for finding the minimum and
saving other legitimate candidates, i.e. those inside R i , in the memory.
As an example to show the algorithm complexity, an FPGA implementation
synthesis result for a 50 Mbps 4

y i − ∑

j

|

i R i , j s j

|

=

× 4 16-QAM depth-first sphere detector is

summarized in Table 2 [ 2 ] .

2.2.5 K-Best Detector Architecture

K -best is another popular algorithm for implementing close-to-ML MIMO detec-
tion [ 15 , 28 , 72 ] . The performance of this scheme is suboptimal compared to ML and