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Papers by Prashant Kumar
DCT based OFDM for Underwater Acoustic Communication
2012 1st International Conference on Recent Advances in Information Technology (RAIT), 2012
Discrete Cosine Transform based Orthogonal Frequency Division Multiplexing (DCT-OFDM) is proposed... more Discrete Cosine Transform based Orthogonal Frequency Division Multiplexing (DCT-OFDM) is proposed for the first time for Underwater Acoustic Communication. Underwater acoustic channels are characterized as doubly spread channels in time and frequency. The orthogonality feature of conventional OFDM is also provided by inverse DCT (IDCT)-DCT structure with the added advantages of reduced implementation area and increased computational speed as only
Underwater acoustic sensor network for early warning generation
2012 Oceans, 2012
There is an ever felt need to create an efficient comprehensive system to tackle natural hazards ... more There is an ever felt need to create an efficient comprehensive system to tackle natural hazards such as Tsunamis, earthquakes, landslides and floods by providing a timely early warning. Underwater wireless sensor network (UWSN) seems to be one promising solution. The success of mobile wireless communication in terms of power efficiency and reliability needs to be repeated with the UWSN for fighting the havoc of nature. An integrated system for early warning generation which would provide information globally is proposed. This paper highlights the physical layer challenges in establishing a reliable, low power consuming and long life UWSN system for early warning generation.
Device-to-Device (D2D) communication fulfils the requirements of 5th generation (5G) communicatio... more Device-to-Device (D2D) communication fulfils the requirements of 5th generation (5G) communication networks such as: low end-to-end latency, higher spectral efficiency, higher data rate and large number of connected devices. But enabling D2D communication in the present cellular network (CN) induces cross-tier interference for cellular user equipment (CUE). This paper proposes a scheme of joint mode selection and power control of D2D user equipment (DUE) to mitigate the cross-tier interference under the assumption that the instantaneous channel gains of user equipments (UEs) and receiver sensitivity of D2D receivers are known to the enhanced-Node B (eNB). Furthermore, it is also assumed that, UEs are in slow fading environment and moving slowly. Mode selection is done on the basis of the instantaneous channel gains, that is, whether UE operates in cellular mode or D2D mode (reuse mode or dedicated mode). Power control of D2D transmitter is done on the basis of D2D receiver sensitivity. The proposed scheme enables more reliable D2D communication with the limited interference to the CN. The proposed scheme uses METIS-2020 channel model for performance evaluation. Simulation results show that the cell sum-rate is significantly increased compared to the conventional CN infrastructure without any major reduction in signal-to-noise-plus-interference ratio (SINR) performance of the cellular users.
—Device-to-Device (D2D) communication is essential for successful implementation of 5th generatio... more —Device-to-Device (D2D) communication is essential for successful implementation of 5th generation (5G) communication networks. D2D communication allows bypassing the enhanced-Node B (eNB) and directly communicating with each other. However it induces interference to the cellular users (CUs) in the D2D enabled cellular network. Controlling the transmission power of D2D users is one of the solutions that maximizes cell throughput, while considering signal-to-noise-plus-interference ratio (SINR) for the CUs at the eNB. This paper proposes a scheme of power control by switching the D2D transmitter on the basis of D2D receiver-sensitivity. Simulation results, have been used to demonstrate the performance improvement, when the proposed scheme is used under the assumptions that the instantaneous channel state information (CSI) and D2D receiver-sensitivity is available at the eNB, and that the D2D pairs are stationary. The proposed scheme is valid for the uplink channel parameters considering communication between eNB and CU. Further, it is also shown that the proposed scheme offers significant increase in the cell sum-rate compared to conventional cellular network infrastructure without any major reduction of SINR performance for the CUs.
—Device-to-Device (D2D) communication is essential for successful implementation of 5th generatio... more —Device-to-Device (D2D) communication is essential for successful implementation of 5th generation (5G) communication networks. D2D communication allows bypassing the enhanced-Node B (eNB) and directly communicating with each other. However it induces interference to the cellular users (CUs) in the D2D enabled cellular network. Controlling the transmission power of D2D users is one of the solutions that maximizes cell throughput, while considering signal-to-noise-plus-interference ratio (SINR) for the CUs at the eNB. This paper proposes a scheme of power control by switching the D2D transmitter on the basis of D2D receiver-sensitivity. Simulation results, have been used to demonstrate the performance improvement, when the proposed scheme is used under the assumptions that the instantaneous channel state information (CSI) and D2D receiver-sensitivity is available at the eNB, and that the D2D pairs are stationary. The proposed scheme is valid for the uplink channel parameters considering communication between eNB and CU. Further, it is also shown that the proposed scheme offers significant increase in the cell sum-rate compared to conventional cellular network infrastructure without any major reduction of SINR performance for the CUs.
Device-to-Device (D2D) communication fulfils the requirements of 5th generation (5G) communicatio... more Device-to-Device (D2D) communication fulfils the requirements of 5th generation (5G) communication networks such as: low end-to-end latency, higher spectral efficiency, higher data rate and large number of connected devices. But enabling D2D communication in the present cellular network (CN) induces cross-tier interference for cellular user equipment (CUE). This paper proposes a scheme of joint mode selection and power control of D2D user equipment (DUE) to mitigate the cross-tier interference under the assumption that the instantaneous channel gains of user equipments (UEs) and receiver sensitivity of D2D receivers are known to the enhanced-Node B (eNB). Furthermore, it is also assumed that, UEs are in slow fading environment and moving slowly. Mode selection is done on the basis of the instantaneous channel gains, that is, whether UE operates in cellular mode or D2D mode (reuse mode or dedicated mode). Power control of D2D transmitter is done on the basis of D2D receiver sensitivity. The proposed scheme enables more reliable D2D communication with the limited interference to the CN. The proposed scheme uses METIS-2020 channel model for performance evaluation. Simulation results show that the cell sum-rate is significantly increased compared to the conventional CN infrastructure without any major reduction in signal-to-noise-plus-interference ratio (SINR) performance of the cellular users.
—Enabling the device-to-device (D2D) communication in the cellular network (CN) induces the probl... more —Enabling the device-to-device (D2D) communication in the cellular network (CN) induces the problem of interference. This paper proposes a scheme of controlling the power of the D2D user equipments (DUEs) by switching D2D transmitter on the basis of receiver-sensitivity. The performance of the proposed scheme has been evaluated in slow fading environment, with the assumptions that the proximity gains, instantaneous gains between base station (BS) and mobile user equipments (UEs) is available at the BS and that the D2D users (DUs) are moving slowly. It has been shown that the cell sum-rate increases significantly compared to conventional CN infrastructure without degrading the performance of the cellular users.
—Device-to-Device (D2D) communication is essential for successful implementation of 5th generatio... more —Device-to-Device (D2D) communication is essential for successful implementation of 5th generation (5G) communication networks. D2D communication allows bypassing the enhanced-Node B (eNB) and directly communicating with each other. However it induces interference to the cellular users (CUs) in the D2D enabled cellular network. Controlling the transmission power of D2D users is one of the solutions that maximizes cell throughput, while considering signal-to-noise-plus-interference ratio (SINR) for the CUs at the eNB. This paper proposes a scheme of power control by switching the D2D transmitter on the basis of D2D receiver-sensitivity. Simulation results, have been used to demonstrate the performance improvement, when the proposed scheme is used under the assumptions that the instantaneous channel state information (CSI) and D2D receiver-sensitivity is available at the eNB, and that the D2D pairs are stationary. The proposed scheme is valid for the uplink channel parameters considering communication between eNB and CU. Further, it is also shown that the proposed scheme offers significant increase in the cell sum-rate compared to conventional cellular network infrastructure without any major reduction of SINR performance for the CUs.
Device-to-Device (D2D) communication fulfils the requirements of 5th generation (5G) communicatio... more Device-to-Device (D2D) communication fulfils the requirements of 5th generation (5G) communication networks such as: low end-to-end latency, higher spectral efficiency, higher data rate and large number of connected devices. But enabling D2D communication in the present cellular network (CN) induces cross-tier interference for cellular user equipment (CUE). This paper proposes a scheme of joint mode selection and power control of D2D user equipment (DUE) to mitigate the cross-tier interference under the assumption that the instantaneous channel gains of user equipments (UEs) and receiver sensitivity of D2D receivers are known to the enhanced-Node B (eNB). Furthermore, it is also assumed that, UEs are in slow fading environment and moving slowly. Mode selection is done on the basis of the instantaneous channel gains, that is, whether UE operates in cellular mode or D2D mode (reuse mode or dedicated mode). Power control of D2D transmitter is done on the basis of D2D receiver sensitivity. The proposed scheme enables more reliable D2D communication with the limited interference to the CN. The proposed scheme uses METIS-2020 channel model for performance evaluation. Simulation results show that the cell sum-rate is significantly increased compared to the conventional CN infrastructure without any major reduction in signal-to-noise-plus-interference ratio (SINR) performance of the cellular users.
Autonomous underwater vehicles (AUVs) are deployed in search and rescue operations wher... more Autonomous underwater vehicles (AUVs) are deployed in search and rescue operations where it is difficult for divers to reach. During the operation a fleet of AUVs communicate among themselves and exchange two type of information. The first includes control signal which has a low-data rate but has a very stringent bit error rate (BER) requirement and the second being the data collected by the AUVs in the form of high resolution video, pictures and important sensor observations, which has a high-data rate but a little relaxed BER constraint. This paper proposes an efficient two-rate data transmission scheme for AUV communication using carrier interferometry (CI) coded direct sequence code-division multiple access (CI/DS-CDMA). The BER performance of the proposed scheme is compared with that of the conventional Walsh Hadamard (WH) coded DS-CDMA in underwater channel and is shown to ensure improved BER performance. For two-rate communication we assume a basic low-data rate (LDR) “R” and a high-data rate (HDR) as “2R” and we further presume that the acceptable BER of LDR is at least an order of magnitude less than that of the HDR. Simulation results show that with CI/DS-CDMA scheme, the high-data rate communication achieves a BER of 3e-4 at 20 dB whereas the low data rate communication reach a BER of 1.76e-5 at 16 dB for a typical underwater channel. The results justify CI/DS-CDMA scheme as a deserving candidate for single rate as well as two-rate underwater acoustic communication.
This paper compares the effectiveness of different spread OFDM techniques with transmit diversity... more This paper compares the effectiveness of different spread OFDM techniques with transmit diversity used for underwater acoustic communications. Spreading by Walsh-
Hadamard codes, discrete Fourier transform, discrete cosine transformand carrier interferom- etry (CI) codes have been combined with the application of space-time and space-frequency transmit diversity in OFDM for underwater acoustic communication. The spreading technique helps overcome frequency-selective and multipath fading and also provides reduced peak-to-average power ratio (PAPR). The application of space time and space frequency coding techniques improves the data rate and reliability of the spread OFDM scheme in terms of bit error rate (BER). Simulation results show that all the spread OFDM schemes show better BER performance in underwater environment when transmit diversity schemes are used. CI spread OFDM with space-frequency block coding shows a BER of 1 e−6 at a signal-to-noise ratio (SNR) of 13.6 dB and is proposed as one of the best scheme. This gain in SNR may be used to further increase the data transmission rate.
This paper presents a comparative study of discrete cosine transform (DCT) spread orthogonal freq... more This paper presents a comparative study of discrete cosine transform (DCT) spread orthogonal frequency division multiplexing (OFDM) with discrete Fourier transform (DFT) spread OFDM, applied to an underwater acoustic (UWA) channel. The UWA channel is characterized as a frequency selective multipath fading channel with long delay spread. Energy compaction property of DCT works well in reducing the peak to average power ratio (PAPR) in UWA channel. It is also shown that DCT spread OFDM has lower computational complexity compared to DFT spread OFDM. The bit error rate (BER) performance has been evaluated for both the schemes. Simulation results show that DCT spread OFDM has a better performance than DFT spread OFDM in UWA channel. A novel scheme of using the null subcarriers to implement complex field repetitive coding in case of DCT spread OFDM is proposed to further reduce the BER.
Conventional orthogonal frequency division multiplexing (OFDM) can reduce errors in underwater ch... more Conventional orthogonal frequency division multiplexing (OFDM) can reduce errors in underwater channels but frequency selective fading can still degrade the data on carriers near deep fade regions. Recently spread-OFDM (SOFDM) which combines the properties of spread spectrum with multicarrier communication has become popular. In this paper spreading by Walsh-Hadamard (WH) codes, discrete Fourier transform (DFT), discrete cosine transform (DCT) and carrier interferometry (CI) codes have been compared for underwater acoustic communication using OFDM. The spreading technique not only helps overcome frequency-selective and multipath fading but also provides reduced peak to average power ratio (PAPR). The performance of this modified OFDM scheme is evaluated in terms of bit error rate (BER) and PAPR. Simulation results show that with CI-SOFDM it is possible to achieve a BER of 1e-4 at 15dB signal to noise ratio. It is also shown that CI-SOFDM offers best PAPR performance. To further improve the BER performance a two level orthogonal spreading by WH followed by CI-SOFDM is also evaluated for underwater communication. The proposed scheme exploits the spreading gain diversity of WH code and phase characteristic property of CI signal to achieve a further gain of 1dB at a BER of 1e-4.
Discrete Cosine Transform based Orthogonal Frequency Division Multiplexing (DCT-OFDM) is proposed... more Discrete Cosine Transform based Orthogonal Frequency Division Multiplexing (DCT-OFDM) is proposed for the first time for Underwater Acoustic Communication. Underwater acoustic channels are characterized as doubly spread channels in time and frequency. The orthogonality feature of conventional OFDM is also provided by inverse DCT (IDCT)-DCT structure with the added advantages of reduced implementation area and increased computational speed as only real calculations is required. This system provide higher peak to average power ratio (PAPR) reduction and achieve better noise immunity and hence better bit error rate (BER) performance than standard OFDM, while maintaining a low implementation cost. Simulation results show noticeable improvement in the performance.
There is an ever felt need to create an efficient comprehensive system to tackle natural hazards ... more There is an ever felt need to create an efficient comprehensive system to tackle natural hazards such as Tsunamis, earthquakes, landslides and floods by providing a timely early warning. Underwater wireless sensor network (UWSN) seems to be one promising solution. The success of mobile wireless communication in terms of power efficiency and reliability needs to be repeated with the UWSN for fighting the havoc of nature. An integrated system for early warning generation which would provide information globally is proposed. This paper highlights the physical layer challenges in establishing a reliable, low power consuming and long life UWSN system for early warning generation.
Orthogonal frequency division multiplexing (OFDM) has been used in underwater communications for ... more Orthogonal frequency division multiplexing (OFDM) has been used in underwater communications for high data rate transmission. Although robust against frequency selective fading, OFDM suffers from high peak to average power ratio (PAPR). PAPR is a serious concern for power constrained underwater sensor nodes. This paper evaluates the performance of Walsh-Hadamard (WH) code spread OFDM in terms of bit error rate (BER) improvement and PAPR reduction. Also the space-time and space-frequency diversity are used to further improve the performance of WH-OFDM in underwater acoustic channel. It is shown by simulation that WH-OFDM with space-frequency coding has the best performance at achievable signal to noise ratio in underwater environment.
This paper investigates the performance of spread orthogonal frequency division multiplexing (SOF... more This paper investigates the performance of spread orthogonal frequency division multiplexing (SOFDM) with space frequency block coding (SFBC) technique for underwater acoustic communication through simulation and semi realistic experimentation. Performance of Walsh-Hadamard code spread OFDM (WHSOFDM) and carrier interferometry code spread (CISOFDM) has been evaluated for underwater acoustic communication along with transmit diversity technique. The spreading technique helps overcome frequency-selectivity and provides reduced peak-to-average power ratio (PAPR) whereas the transmit diversity technique improves the data rate and reliability. CISOFDM with SFBC offers a SNR gain of 2.4 dB for a bit-error-rate (BER) of 1e- 6 over WHSOFDM with SFBC. The present work also demonstrates the design of a low cost experimental setup (testbed) to perform a large number of experiments related to underwater communication and prototype algorithm testing. A simple two-transmit-one receive SFBC-CISOFDM scheme is used to transmit images through the underwater channel to validate the simulation.
Underwater acoustic communication is essential in applications like remote control in the offshor... more Underwater acoustic communication is essential in applications like remote control in the offshore oil industry, pollution monitoring in environmental systems, collection of scientific data recorded at ocean-bottom stations, disaster detection and early warning and underwater surveillance. Research on underwater wireless communication techniques plays a vital role in further exploring oceans and other marine environments. There has been an extensive growth in the volume of literature for underwater acoustic (UWA) communication but still it remains to be one of the most challenging areas of wireless communication. Over the years attention has turned on applying modified versions of multicarrier (MC) communication to underwater channel. This paper reviews the recent developments in the area of UWA communication related to multicarrier communication and particularly to orthogonal frequency division multiplexing (OFDM) with respect to applied, theoretical and simulation studies. An attempt has been made to present a compact yet exhaustive literature survey that will serve as a standard reference for researchers working in the area. Stress has been laid on the physical layer issues as it works as the basic foundation of any network. The focus areas of research activities have been identified and a summary of the ongoing activities and future trends has been presented.
This paper evaluates the performance of differentially encoded quadrature phase shift keying (DQP... more This paper evaluates the performance of differentially encoded quadrature phase shift keying (DQPSK) modulated orthogonal frequency division multiplexing (OFDM) for underwater acoustic (UWA) communication. The combination of OFDM and the non-coherent detection scheme maintains the receiver design simple, reliable and pectrally efficient. QPSK helps achieve higher data rate as two bits are sent over each sub-carrier. Further differential coding is chosen as it does not require phase coherent reference signal at the receiver, which helps to overcome the detrimental effect of the random phase in the received signal. An added advantage of using DQPSK is that for slow Doppler frequency shift, the phase difference remains unaffected and the data can be retrieved. The performance of DQPSK OFDM is studied over a typical underwater channel through extensive computer simulation and a semi-realistic experiment. DQPSK OFDM scheme is used to transmit an image through the underwater channel in an experimental tank to validate the simulation. Furthermore selection combining technique is also implemented at the receiver to enhance the system reliability and performance. With two hydrophones at the receiving end and diversity combining it is possible to achieve a bit error rate (BER) of 2e-4 with 512 sub-carrier and 2e-5 with 256 sub-carriers respectively at a signal-to-noise ratio (SNR) of 21 dB.
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Papers by Prashant Kumar
Hadamard codes, discrete Fourier transform, discrete cosine transformand carrier interferom- etry (CI) codes have been combined with the application of space-time and space-frequency transmit diversity in OFDM for underwater acoustic communication. The spreading technique helps overcome frequency-selective and multipath fading and also provides reduced peak-to-average power ratio (PAPR). The application of space time and space frequency coding techniques improves the data rate and reliability of the spread OFDM scheme in terms of bit error rate (BER). Simulation results show that all the spread OFDM schemes show better BER performance in underwater environment when transmit diversity schemes are used. CI spread OFDM with space-frequency block coding shows a BER of 1 e−6 at a signal-to-noise ratio (SNR) of 13.6 dB and is proposed as one of the best scheme. This gain in SNR may be used to further increase the data transmission rate.