Abdel-karim Ajami

PAPR reduction in LTE-Advanced carrier aggregation using low-complexity joint interleaving technique

The demand for high data rates in both the uplink and the downlink has motivated the use of carrier aggregation (CA) of several portions of the spectrum up to 100 MHz in LTE-Advanced, while maintaining backward compatibility with LTE release 8. One of the main practical challenges that comes with CA is the severe increase of peak-to-average-power-ratio (PAPR) of the corresponding generated time-domain OFDM signal, thus affecting the power amplifier (PA) efficiency, and hence the transmission coverage. This paper proposes a low-complexity joint interleaving technique to reduce the PAPR of carrier aggregated signals. Several CA scenarios were analyzed using our proposed technique. Simulation results demonstrate that our proposed technique can achieve the same PAPR reduction performance as that of the partial selective mapping (PSLM) technique with 66% reduction in terms of real multiplication and addition operations for the case of three aggregated component carriers (CCs).

A Low-Complexity PAPR Reduction Technique for LTE-Advanced Uplink with Carrier Aggregation

In LTE-Advanced, carrier aggregation (CA) is a key enabling technique to increase the peak data rates of users and enhance the mobility management in heterogeneous networks (HetNets) using dual connectivity solutions. Several CA schemes have been proposed with a maximum of five LTE Release 8 component carriers (CCs) where the NxSC-FDMA has been chosen as the bandwidth extension scheme for the uplink. This enables the extension of the bandwidth allocated to a user up to 100 MHz while maintaining backward compatibility with LTE release 8 legacy users. However, CA leads to a severe increase in the peak-to-average-power ratio (PAPR) of the aggregated time domain NxSC-FDMA signal at the user equipment (UE). This is an important issue as it affects the power amplifier (PA) efficiency and hence the coverage of transmissions. In this paper, we propose a low- complexity post-IFFT technique to reduce the PAPR of carrier aggregated NxSC-FDMA signals in the uplink of LTE-Advanced. Several case studies of CA were analyzed by using the proposed technique. Simulation results show that the PAPR improvement is 2.5 dB for the case of 2 CCs at only about 4% of the complexity required by the partial selective mapping (PSLM) technique to achieve the same PAPR reduction.

On The Modeling and Analysis of Uplink and Downlink IEEE 802.11ax Wi-Fi With LTE in Unlicensed Spectrum

The growing demand on data to enhance the user experience has motivated research toward increasing the efficiency of spectrum utilization by extending cellular technology, such as LTE, toward unlicensed bands. In order to study the fair coexistence of LTE and Wi-Fi, we consider the IEEE 802.11ax Wi-Fi standard, where we use stochastic geometry to model and analyze the coexistence of LTE with simultaneous uplink and downlink IEEE 802.11ax transmissions. Mainly, we consider LTE with continuous transmissions (no protocol change), LTE with discontinuous transmissions (LTE-U), and licensed-assisted access (LAA) coexistence mechanisms. In addition, we focus on single unlicensed frequency band transmissions, where the locations of Wi-Fi access points, Wi-Fi stations (users), and LTE eNodeBs (eNBs) are modeled as three independent homogeneous Poisson point processes. Then, we derive analytical expressions for a set of performance metrics, which are the medium access probability, signal-to-interference-plus-noise ratio coverage probability, density of successful transmissions, and Shannon throughput probability for both uplink and downlink of IEEE 802.11ax in addition to LTE. Our analysis quantifies both single-user and multi-user operation modes of the IEEE802.11ax and show that LTE-U or LAA can be a good neighbor for IEEE 802.11ax for different traffic types.

KLT-based PAPR reduction technique for LTE-Advanced uplink with carrier aggregation

In LTE-Advanced, carrier aggregation (CA) allows the extension of the bandwidth allocated to a certain user up to 100 MHz. In particular, the NxSC-FDMA has been selected as the uplink extension scheme. However, one of the main practical challenges that comes with CA is the severe increase in the peak-to-average-power ratio (PAPR) of the aggregated time domain NxSC-FDMA signal. The PAPR increase is an important issue as it affects the efficiency of the power amplifier (PA) at the user equipment (UE) and equivalently the transmission coverage of the LTE-Advanced system. In this paper we propose a PAPR reduction technique based on the well-known Karhunen-Loeve Transform (KLT) to reduce the PAPR of the NxSC-FDMA signals. Several CA scenarios were analyzed using the proposed technique and simulation results show that the performance of the PAPR has improved by 1.5 dB in case of carrier aggregation of two CCs.

LTE frequency one re-use factor: Would it be an efficient solution for the unlicensed bands? A stochastic geometry analysis

With the increasing demand on higher data rates to enhance the user experience, one possible solution would be to extend the cellular technology such as LTE toward the unlicensed bands. Initially, LTE was designed based on the frequency re-use factor of one and which has lead to higher capacity in several deployment scenarios. This happens when LTE exclusively uses the licensed spectrum where interference can be controlled. On the other hand, when LTE uses the unlicensed spectrum, other technologies such as WiFi will coexist and hence LTE will be subject to uncontrolled interference while it is expected to achieve a fair coexistence with such technologies. Given these constraints, we discuss in this paper the utilization of frequency re-use factor of one for LTE in the unlicensed band. In this case and subject to regulations of utilizing unlicensed bands, LTE will use the Listen before talk (LBT) mechanism with other radio access technologies. Thus, using tools from stochastic geometry, we model and analyze the effect of such scenario while comparing it to the case where LTE considers LBT mechanism with other LTE transmissions. Our analysis shows interesting performance gains that can be achieved by LTE in terms of rate coverage probability.

A stochastic optimization technique for PAPR reduction in the uplink of LTE-Advanced with carrier aggregation

The ever increase in the demand on peak data rates due to emerging services and applications has motivated the use of carrier aggregation (CA) as a key enabling technique to increase the bandwidth of users. CA allows the users to utilize both licensed and unlicensed spectrum simultaneously. However one of the main practical challenges that comes with CA is the severe increase in the peak-to-average-power ratio (PAPR) of the aggregated time domain N×SC-FDMA signal. This issue affects the efficiency of the power amplifier (PA) at the user equipment (UE) in the uplink and hence the transmission coverage is reduced. In this paper, we propose a stochastic optimization technique to reduce the PAPR of N×SC-FDMA signals. Several CA scenarios were analyzed where experimental results show that the proposed technique outperforms the random circular shifting technique and can provide an average coverage gain of 40% for the case of 2 CCs.

A two stage PAPR reduction technique for the uplink of LTE-Advanced with carrier aggregation

Carrier aggregation (CA) is a key enabling technique to increase the bandwidth of users in order to meet the increasing demand on peak data rates for emerging services and applications. However one of the main practical challenges that comes with CA is the severe increase in the peak-to-average-power ratio (PAPR) of the aggregated time domain NxSC-FDMA signal. This issue is critical for the user equipment (UE) in the uplink as it affects the efficiency of the power amplifier (PA) and hence the transmission coverage. In this paper, a novel two stage PAPR reduction scheme based on frequency spacing aware Discrete Fourier Transform (FSA-DFT) is proposed. Several CA scenarios were analyzed using the proposed technique. Experimental results show that the proposed technique provides a significant reduction in the PAPR of aggregated NxSC-FDMA signal.

A faulty node detection scheme for wireless sensor networks that use data aggregation for transport

This paper presents a faulty node detection approach for wireless sensor networks that aggregate measurement data on their way toward the sink base station. The approach is based on the idea of commanding sensor nodes on the aggregation paths to temporarily stop including their readings in the received aggregated readings from their upstream neighbors. The scheme is dependent on the ability of the sink to detect faulty nodes through changes in the received aggregated readings at the sink using a Markov Chain Controller MCC. The algorithm that is run in the sink uses the MCC to assign a state to each sensor node based on transitions that are triggered by receiving aggregated path readings, and accordingly deduces the nodes that may be faulty. The experimental results show at least 98% detection rate at the cost of reasonable detection delays and generated wireless network traffic. Copyright

An approximation for the distribution of the peak-to-average power ratio in carrier-aggregated OFDM signals using level crossing rate analysis

Carrier Aggregation started to appear since release 10 of LTE, and offers higher data rates, but at the cost of increased Peak-to-Average-Power-Ratio (PAPR). This paper studies the distribution of PAPR through analyzing the Crest Factor (CF) which is the square root of the PAPR of the Carrier Aggregated OFDM (CA-OFDM) signals used in the downlink of LTE-A. Although the base station is not power constrained, the increased PAPR can adversely affect performance in terms of energy efficiency and coverage. We model the distribution of the CF by adopting the Level Crossing Rate analysis to approximate the peak distribution of the CA-OFDM signal which can be characterized as a band-limited complex Gaussian process. The expression of the distribution is derived for an arbitrary number of component carriers for both contiguous and non-contiguous aggregation, where simulations show good agreement with the derived analytical expressions. The derived expression is applied to model the Selective Mapping technique used for PAPR reduction.

Fairness in future Licensed Assisted Access (LAA) LTE networks: What happens when operators have different channel access priorities?

The growing demand on data to enhance the user experience has motivated research toward increasing the efficiency of spectrum utilization by extending cellular technology such as LTE toward unlicensed bands. In order to study the effect of channel access priorities on coexistence of several LAA networks, we consider load based equipment (LBE) based MAC protocol where we use stochastic geometry to model and analyze the coexistence of three LTE-LAA networks with persistent downlink transmissions. Mainly, we focus on single unlicensed frequency band transmissions. The locations of LAA eNodeBs (eNBs) for the three operators are modeled as three independent homogeneous Poisson point processes. Furthermore, we derive analytical closed form expressions for a set of performance metrics which are the medium access probability (MAP), signal-to-interference-plus-noise ratio (SINR) coverage probability, and rate coverage probability. Our analysis shows the impact of channel access priorities used by different operators on their network performance.