8 research outputs found
Binary-Tree Encoding for Uniform Binary Sources in Index Modulation Systems
The problem of designing bit-to-pattern mappings and power allocation schemes
for orthogonal frequency-division multiplexing (OFDM) systems that employ
subcarrier index modulation (IM) is considered. We assume the binary source
conveys a stream of independent, uniformly distributed bits to the pattern
mapper, which introduces a constraint on the pattern transmission probability
distribution that can be quantified using a binary tree formalism. Under this
constraint, we undertake the task of maximizing the achievable rate subject to
the availability of channel knowledge at the transmitter. The optimization
variables are the pattern probability distribution (i.e., the bit-to-pattern
mapping) and the transmit powers allocated to active subcarriers. To solve the
problem, we first consider the relaxed problem where pattern probabilities are
allowed to take any values in the interval [0,1] subject to a sum probability
constraint. We develop (approximately) optimal solutions to the relaxed problem
by using new bounds and asymptotic results, and then use a novel heuristic
algorithm to project the relaxed solution onto a point in the feasible set of
the constrained problem. Numerical analysis shows that this approach is capable
of achieving the maximum mutual information for the relaxed problem in low and
high-SNR regimes and offers noticeable benefits in terms of achievable rate
relative to a conventional OFDM-IM benchmark.Comment: 18 pages, 16 figures, 2 table
Enhanced Huffman Coded OFDM with Index Modulation
In this paper, we propose an enhanced Huffman coded orthogonal
frequency-division multiplexing with index modulation (EHC-OFDM-IM) scheme. The
proposed scheme is capable of utilizing all legitimate subcarrier activation
patterns (SAPs) and adapting the bijective mapping relation between SAPs and
leaves on a given Huffman tree according to channel state information (CSI). As
a result, a dynamic codebook update mechanism is obtained, which can provide
more reliable transmissions. We take the average block error rate (BLER) as the
performance evaluation metric and approximate it in closed form when the
transmit power allocated to each subcarrier is independent of channel states.
Also, we propose two CSI-based power allocation schemes with different
requirements for computational complexity to further improve the error
performance. Subsequently, we carry out numerical simulations to corroborate
the error performance analysis and the proposed dynamic power allocation
schemes. By studying the numerical results, we find that the depth of the
Huffman tree has a significant impact on the error performance when the
SAP-to-leaf mapping relation is optimized based on CSI. Meanwhile, through
numerical results, we also discuss the trade-off between error performance and
data transmission rate and investigate the impacts of imperfect CSI on the
error performance of EHC-OFDM-IM
Lexicographic Codebook Design for OFDM with Index Modulation
In this paper, we propose a novel codebook design scheme for orthogonal frequency-division multiplexing with index modulation (OFDM-IM) to improve system performance. The optimization process can be implemented efficiently by the lexicographic ordering principle. By applying the proposed codebook design, all subcarrier activation patterns with a fixed number of active subcarriers will be explored. Furthermore, as the number of active subcarriers is fixed, the computational complexity for estimation at the receiver is reduced and the zero-active subcarrier dilemma is solved without involving complex higher layer transmission protocols. It is found that the codebook design can potentially provide a trade-off between diversity and transmission rate. We investigate the diversity mechanism and formulate three diversity-rate optimization problems for the proposed OFDMIM system. Based on the genetic algorithm (GA), the method of solving these formulated optimization problems is provided and verified to be effective. Then, we analyze the average block error rate (BLER) and bit error rate (BER) of OFDM-IM systems applying the codebook design. Finally, all analyses are numerically verified by Monte Carlo simulations. In addition, a series of comparisons are provided, by which the superiority of the codebook design is thereby confirmed
Lexicographic codebook design for OFDM with index modulation
In this paper, we propose a novel codebook design scheme for orthogonal frequency-division multiplexing with index modulation (OFDM-IM) to improve system performance. The optimization process can be implemented efficiently by the lexicographic ordering principle. By applying the proposed codebook design, all subcarrier activation patterns with a fixed number of active subcarriers will be explored. Furthermore, as the number of active subcarriers is fixed, the computational complexity for estimation at the receiver is reduced and the zero-active subcarrier dilemma is solved without involving complex higher layer transmission protocols. It is found that the codebook design can potentially provide a tradeoff between diversity and transmission rate. We investigate the diversity mechanism and formulate three diversity-rate optimization problems for the proposed OFDM-IM system. Based on the genetic algorithm, the method of solving these formulated optimization problems is provided and verified to be effective. Then, we analyze the average block error rate and bit error rate of the OFDM-IM systems applying the codebook design. Finally, all analyses are numerically verified by the Monte Carlo simulations. In addition, a series of comparisons are provided, by which the superiority of the codebook design is confirmed