Figure 2: Transmitter data flow (Symbols are 32 bit complex numbers)
Figure 3: Receiver data flow ( Symbols are 32 bit complex numbers)
Guard Interval Insertion: The 64 complex outputs of
the IFFT kernel are extended to form an array of 80
complex numbers by copying the last 16 outputs as the
guard interval prior to the first IFFT output. As previously
mentioned, this kernel is needed to avoid ISI.
Training Symbol Insertion: To help the receiver esti-
mate the effects of noise and distortion in wireless channels,
the transmitter inserts small, fixed length of training
symbols before transmission. In Figure 2 and 3, the kernels
used for signal recovery are filled in gray color.
2.3.2 Kernels in the Receiver
We present explanations for the only two kernels in the
receiver without counterparts in the transmitter.
Time and Frequenc y Recovery: This kernel is com-
posed of packet detection, time synchronization, and
frequency correction. Packet detection roughly identifies
transmitted signals and time synchronization exactly
distinguishes transmitted signals from noise signals.
Frequency correction estimates frequency error in the orig-
inal t ransmitted signals, and recovers the original frequency.
Channel Estimation: As explained in Section 2.1,
there are multiple sub-carriers used by OFDM technology.
Each sub-carrier is located at a particular frequency.
Wireless channels affect on these sub-carriers to varying
degrees. In the ideal channel case, this gain is 1 for all
sub-carriers. However, for the real channel environment,
the channel esti m ation block estimates the amount of gain
change, and recovers the original gain for each sub-carrier.
Dynamic reconfiguration can be used in MIMO-OFDM
systems to change data rate, increase diversity, or increase
range. This idea is applied to three kernels: puncturing
(depuncturing), QAM mapping (QAM demapping) , and
parsing (deparsing). A detailed analysis of dynamic
reconfiguration is presented in Section 4.
3 P ipelined Architecture for
MIMO-OFDM
3.1 Definitions
Before we describe our proposed architecture, we briefly
define several terms and notations used in this paper.
N × M MIMO-OFDM : N indicates the number of
transmitter antennas and M indicates the number of
receiver antennas, respectively. For example, 3 × 3 MIMO-
OFDM has 3 transmitter antennas and 3 receiver antennas
as shown in Figure 1.
Baseline MIMO-OFDM : A MIMO-OFDM system that
uses as many IFFT blocks (or FFT blocks) as antennas in
the transmitter (or receiver). This simple idea conforms
with t he basic theory of MIMO-OFDM, which suggests
that multiple data streams are modulated by their own
FFT blocks [22].
Way: The number of antennas that can be supported by
the proposed pipelined architecture with one FFT. For
example, 2-W ay means that the proposed system achieves
the same data rate as the baseline 2 × 2 MIMO-OFDM
system with two FFT blocks, as shown in Figure 5.
Pipeline sta ge period : The period of a pipeline stage.
In our pipelined architecture, this period is 4 µsec given by
existing OFDM standard [1]. The number of clocks (C
P ipe
)
for this period varies with the system clock frequency. For