4 research outputs found
L2 Orthogonal Space Time Code for Continuous Phase Modulation
To combine the high power efficiency of Continuous Phase Modulation (CPM)
with either high spectral efficiency or enhanced performance in low Signal to
Noise conditions, some authors have proposed to introduce CPM in a MIMO frame,
by using Space Time Codes (STC). In this paper, we address the code design
problem of Space Time Block Codes combined with CPM and introduce a new design
criterion based on L2 orthogonality. This L2 orthogonality condition, with the
help of simplifying assumption, leads, in the 2x2 case, to a new family of
codes. These codes generalize the Wang and Xia code, which was based on
pointwise orthogonality. Simulations indicate that the new codes achieve full
diversity and a slightly better coding gain. Moreover, one of the codes can be
interpreted as two antennas fed by two conventional CPMs using the same data
but with different alphabet sets. Inspection of these alphabet sets lead also
to a simple explanation of the (small) spectrum broadening of Space Time Coded
CPM
Full Rate L2-Orthogonal Space-Time CPM for Three Antennas
To combine the power efficiency of Continuous Phase Modulation (CPM) with
enhanced performance in fading environments, some authors have suggested to use
CPM in combination with Space-Time Codes (STC). Recently, we have proposed a
CPM ST-coding scheme based on L2-orthogonality for two transmitting antennas.
In this paper we extend this approach to the three antennas case. We
analytically derive a family of coding schemes which we call Parallel Code
(PC). This code family has full rate and we prove that the proposed coding
scheme achieves full diversity as confirmed by accompanying simulations. We
detail an example of the proposed ST codes that can be interpreted as a
conventional CPM scheme with different alphabet sets for the different transmit
antennas which results in a simplified implementation. Thanks to
L2-orthogonality, the decoding complexity, usually exponentially proportional
to the number of transmitting antennas, is reduced to linear complexity
Separable Implementation of L2-Orthogonal STC CPM with Fast Decoding
In this paper we present an alternative separable implementation of
L2-orthogonal space-time codes (STC) for continuous phase modulation (CPM). In
this approach, we split the STC CPM transmitter into a single conventional CPM
modulator and a correction filter bank. While the CPM modulator is common to
all transmit antennas, the correction filter bank applies different correction
units to each antenna. Thereby desirable code properties as orthogonality and
full diversity are achievable with just a slightly larger bandwidth demand.
This new representation has three main advantages. First, it allows to easily
generalize the orthogonality condition to any arbitrary number of transmit
antennas. Second, for a quite general set of correction functions that we
detail, it can be proved that full diversity is achieved. Third, by separating
the modulation and correction steps inside the receiver, a simpler receiver can
be designed as a bank of data independent inverse correction filters followed
by a single CPM demodulator. Therefore, in this implementation, only one
correlation filter bank for the detection of all transmitted signals is
necessary. The decoding effort grows only linearly with the number of transmit
antennas
L2 OSTC-CPM: Theory and design
The combination of space-time coding (STC) and continuous phase modulation
(CPM) is an attractive field of research because both STC and CPM bring many
advantages for wireless communications. Zhang and Fitz [1] were the first to
apply this idea by constructing a trellis based scheme. But for these codes the
decoding effort grows exponentially with the number of transmitting antennas.
This was circumvented by orthogonal codes introduced by Wang and Xia [2].
Unfortunately, based on Alamouti code [3], this design is restricted to two
antennas. However, by relaxing the orthogonality condition, we prove here that
it is possible to design L2-orthogonal space-time codes which achieve full rate
and full diversity with low decoding effort. In part one, we generalize the
two-antenna code proposed by Wang and Xia [2] from pointwise to
L2-orthogonality and in part two we present the first L2-orthogonal code for
CPM with three antennas. In this report, we detail these results and focus on
the properties of these codes. Of special interest is the optimization of the
bit error rate which depends on the initial phase of the system. Our simulation
results illustrate the systemic behavior of these conditions