Pavan Kumar Vitthaladevuni

A recursive algorithm for the exact BER computation of generalized hierarchical QAM constellations

Hierarchical constellations offer a different degree of protection to the transmitted messages according to their relative importance. As such, they find interesting application in digital video broadcasting systems as well as wireless multimedia services. Although a great deal of attention has been devoted in the literature to the study of the bit error rate (BER) performance of uniform quadrature amplitude modulation (QAM) constellations, very few results were published on the BER performance of hierarchical QAM constellations. We obtain exact and generic expressions in M for the BER of the generalized hierarchical M-PAM (pulse amplitude modulation) constellations over additive white Gaussian noise (AWGN) and fading channels. We also show how these expressions can be extended to generalized hierarchical M-QAM constellations (square and rectangular). For the AWGN case, these expressions are in the form of a weighted sum of complementary error functions and are solely dependent on the constellation size M, the carrier-to-noise ratio, and a constellation parameter which controls the relative message importance. Because of their generic nature, these new expressions readily allow numerical evaluation for various cases of practical interest.

Adaptive hierarchical modulation for simultaneous voice and multiclass data transmission over fading channels

In this paper, a new technique for simultaneous voice and multiclass data transmission over fading channels using adaptive hierarchical modulation is proposed. According to the link quality, the proposed scheme changes the constellation size as well as the priority parameters of the hierarchical signal constellations and assigns available subchannels (i.e., different bit positions) to different kinds of bits. Specifically, for very bad channel conditions, it only transmits voice with binary phase-shift keying (BPSK). As the channel condition improves, a variable-rate adaptive hierarchical M-ary quadrature amplitude modulation (M-QAM) is used to increase the data throughput. The voice bits are always transmitted in the lowest priority subchannel (i.e., the least significant bit (LSB) position) of the quadrature (Q) channel of the hierarchical M-QAM. The remaining (log2M-1) subchannels, called data subchannels, are assigned to two different classes of data according to the selected priority parameters. Closed-form expressions as well as numerical results for outage probability, achievable spectral efficiency, and average bit error rate (BER) for voice and data transmission over Nakagami-m fading channels are presented. The adaptive techniques employing hybrid binary shift keying (BPSK)/M-ary AM (M-AM) and uniform M-QAM for simultaneous voice and two different classes of data transmission are also extended. Compared to the extended schemes, the new proposed scheme is spectrally more efficient for data transmission, while keeping the same outage probability for voice and data (both classes) as the scheme employing BPSK/M-AM. The new scheme also provides, as a by-product, a spectrally efficient way of transmitting voice and a single-class data

Exact BER computation for cross QAM constellations

When the number of bits per symbol is odd, the peak and average power of transmission can be reduced by using cross quadrature amplitude modulations (QAMs) instead of rectangular QAMs. However, since perfect Gray coding is not possible for cross QAMs, using Smith-style Gray coding, this paper derives the exact bit error rate (BER) for cross QAM constellations over additive white Gaussian noise (AWGN) and Rayleigh fading channels.

A closed-form expression for the exact BER of generalized PAM and QAM constellations

We derive an explicit closed-form expression for the exact bit-error rate (BER) computation of generalized hierarchical M-ary pulse amplitude modulations over additive white Gaussian noise (AWGN) and fading channels. This expression can also be used to obtain the exact BER of generalized hierarchical quadrature amplitude modulations (square and rectangular). For the AWGN case, these expressions are in the form of a weighted sum of complementary error functions, and are solely dependent on the constellation size M, the carrier-to-noise ratio, and a constellation parameter which controls the relative message importance.

BER computation of generalized QAM constellations

Based on a Karnaugh map style Gray coding of constellations, we derive a recursive algorithm for the exact bit error rate computation of generalized hierarchical M-ary pulse amplitude modulations (PAM) over additive white Gaussian noise (AWGN) and fading channels. We also show how this algorithm can be extended to generalized hierarchical quadrature amplitude modulation constellations (square and rectangular). For the AWGN case, these expressions are in the form of a weighted sum of complementary error functions and are solely dependent on the constellation size M, the carrier-to-noise ratio, and a constellation parameter which controls the relative message importance.

Effect of imperfect phase and timing synchronization on the error rate performance of PSK modulations

A great deal of attention has been devoted in the recent literature to the study of the symbol error rate (SER) and bit error rate (BER) performance of phase shift keyed (PSK) constellations due to their high spectral efficiency and constant envelope nature. It is well known that an error in phase or timing synchronization affects the probability of correct decisions at the receiver. This problem becomes much more significant as data rates increase and the corresponding symbol durations decrease. We look into this problem and analyze the exact SER and BER performance of uniform and hierarchical PSK constellations under imperfect phase or timing synchronization over additive white Gaussian noise (AWGN) channels. These expressions are in the form of a weighted sum of Pawula functions and are solely dependent on the constellation size, M, the carrier-to-noise ratio (CNR), the phase/timing error, and, for the case of hierarchical constellations, a priority vector which controls the relative message importance. Because of their purely exponential dependence on the CNR, these expressions can easily be generalized to fading conditions with and without diversity reception. In addition, due to their generic nature, these new expressions readily allow numerical evaluation for various cases of practical interest.

Performance Analysis of Dual-Carrier HSDPA

The newly standardized Dual-Carrier HSDPA offers two-carrier aggregation on the downlink. In this paper, we investigate the performance gains from the dual-carrier operations with both full buffer and bursty traffic models. With full buffer traffic, dual-carrier offers dynamic load balancing and increase in user data rate, system capacity and spectral efficiency. All the users throughout the system enjoy the data rate increase. With bursty traffic, dual-carrier provides substantial gain in user experience measured by burst rates or latency under all loading conditions. Moreover, the gain with bursty traffic is universal not only for all the users but also for a very wide range of scheduling algorithms. Our results are based on analysis and extensive simulations. Design issues are also addressed in this paper.

Exact BER computation for the cross 32-QAM constellation

When the number of bits per symbol is odd, the peak and average power of transmission can be reduced by using cross quadrature amplitude modulations (QAMs) instead of rectangular QAMs. Since perfect Gray coding is not possible for cross QAMs, using Smith-style Gray coding, we derive in this paper the exact bit error rate (BER) for the cross 32-QAM constellation over additive white Gaussian noise (AWGN) and Rayleigh fading channels.

Exact BER computation of generalized hierarchical PSK constellations

Hierarchical constellations offer a different degree of protection to the transmitted messages according to their relative importance. As such they found interesting application in digital video broadcasting systems as well as wireless multimedia services. Although a great deal of attention has been devoted in the literature to the study of the bit error rate (BER) performance of uniform phase shift keyed (PSK) constellations, very few results were published on the BER performance of hierarchical PSK constellations. We obtain exact and generic expressions in M for the BER of the generalized hierarchical M-PSK constellations over additive white Gaussian noise (AWGN) and fading channels. For the AWGN case, these expressions are in the form of a weighted sum of Pawula (1982) F-functions and are solely dependent on the constellation size M, the carrier-to-noise ratio, and a constellation parameter which controls the relative message importance. Because of their generic nature, these new expressions readily allow numerical evaluation for various cases of practical interest.

Performance Gains of Single-Frequency Dual-Cell HSDPA

In this paper, we will study the scheme of Single-Frequency Dual-Cell HSDPA (SF-DC HSDPA) which is introduced to simultaneously transmit two separate packet streams from two cells to a mobile. The inter-stream interference is suppressed by the linear-MMSE equalizer at the mobile. In the simple implementation studied in this paper, the schedulers at the two cells are independent without information exchange. Our study is based on both analysis and simulations. SF-DC HSDPA offers significantly higher data rates to users in the handover region. It also achieves dynamic load balancing in terms of resource utilizations across cells. Furthermore, all these gains can be obtained without degrading the performance of users not in handover and the legacy users. The gain from SF-DC is particularly substantial for users in heavily loaded cells surrounded by lightly loaded neighboring cells. In addition, such gain can increase with loading at a given loading ratio between the heavily loaded and lightly loaded cells. SF-DC is easy to implement with only incremental complexity to the current mobile and network equipment.