Long Term Evolution Specification Research Articles

Tunable Frequency-Division Duplex RF Front End Using Electrical Balance and Active Cancellation

This paper presents a novel, tunable, frequency-division duplexing radio frequency (RF) front end that combines passive and active self-interference (SI) cancellation. An electrical-balance duplexer is used to passively cancel transmitter noise in the receive band, and an active canceller is employed to suppress SI in the transmit (Tx)-band. Subsystem specifications are developed, and a system-level analysis of noise and SI powers in this novel architecture is provided, thereby illustrating its operation. A proof-of-concept demonstrator, built from a software-defined radio and discrete RF components, has been characterized across a range of duplex configurations in the 700–950-MHz range and also at 1900 (Long-Term Evolution (LTE) band 3) and 2600 MHz (LTE band 7). The prototype achieves an impressive 6.0–7.4-dB noise figure in the presence of a +27-dBm LTE uplink Tx blocker for duplex separations of 47.5 MHz and above. The duplexer has also been tested against reference sensitivity test cases defined in the 3GPP LTE specification, demonstrating specification compliant sensitivity in LTE bands 28 (700 MHz), 3, and 7.

A Comparative Study of PMI/RI Selection Schemes for LTE/LTEA Systems

This paper presents a joint calculation of the precoding matrix indicator (PMI) and rank indicator (RI) in multiple-input multiple-output (MIMO) downlink third generation partnership project (3GPP) universal mobile telecommunications system (UMTS)/long-term evolution (LTE) systems. The standard codebook based precoding is used where the mobile station estimates and sends some measures related to the channel state information to the base station for link adaptation purpose. We study the system performance using link-level simulation under realistic assumptions. Specifically, we use K-best MIMO decoding in the presence of perfect and imperfect estimation of the channel and the noise variance, as well as white and colored noise plus interference defined by the 3GPP LTE specification documents. Similar to some previous results, our method for calculating the PMI/RI is based on maximizing the mutual information between the transmitted and received symbols with respect to the precoding matrix. We evaluate the system performance using two channel measures when computing the mutual information. The first measure is the estimated channel whereas the second one is the estimated channel covariance matrix. Although these two measures have been used in different literature, there have not been conclusive results on which one should be used in different practical scenarios. We assess the system performance using Monte Carlo simulations and compare different test cases, e.g., 3GPP channel models, wideband, and subband PMI/RI calculation, white/color noise plus interference, etc. We then conclude our work with technical recommendations for different scenarios.

An isolation-enhanced quad-element antenna using suspended solid wires for LTE small-cell base stations

This paper presents a multiple-input-multiple-output (MIMO) antenna that has four unit elements enabled by an isolation technique for long-term-evolution (LTE) small-cell base stations. While earlier studies on MIMO base-station antennas cope with either a lower LTE band (698–960 MHz) or an upper LTE band (1710–2690 MHz), the proposed antenna meets the full LTE specification, yet it uses the maximum number of unit elements to increase channel capacity. The antenna configuration is optimized for good impedance matching and high radiation efficiency. In particular, as the spacing between unit elements is so small that severe mutual coupling occurs, we propose a simple structure with extremely low costs to enhance the isolation. By using suspended solid wires interconnecting the position having strong coupled current of two adjacent elements, an isolation enhancement of 37 dB is achieved. Although solid wires inherently aim at direct-current applications, this work successfully employs such a low-cost technique to microwave antenna development. Experimental results have validated the design guidelines and the proposed configuration, showing that antenna performances including impedance matching, isolation, radiation features, signal correlation, and channel capacity gain are highly desired for LTE small-cell base stations.

Adaptive Subframe Allocation for Next Generation Multimedia Delivery Over Hybrid LTE Unicast Broadcast

The continued global roll-out of long term evolution (LTE) networks is providing mobile users with perpetually increasing ubiquitous access to a rich selection of high quality multimedia. Interactive viewing experiences including 3-D or free-viewpoint video require the synchronous delivery of multiple video streams. This paper presents a novel hybrid unicast broadcast synchronisation (HUBS) framework to synchronously deliver multi-stream content. Previous techniques on hybrid LTE implementations include staggered modulation and coding scheme grouping, adaptive modulation coding or implementing error recover techniques; the work presented here instead focuses on dynamic allocation of resources between unicast and broadcast, improving stream synchronisation as well as overall cell resource usage. Furthermore, the HUBS framework has been developed to work within the limitations imposed by the LTE specification. Performance evaluation of the framework is performed through the simulation of probable future scenarios, where a popular live event is broadcast with stereo 3-D or multi-angle companion views interactively offered to capable users. The proposed framework forms a “HUBS group” that monitors the radio bearer queues to establish a time lead or lag between broadcast and unicast streams. Since unicast and broadcast share the same radio resources, the number of subframes allocated to the broadcast transmission are then dynamically increased or decreased to minimise the average lead/lag time offset between the streams. Dynamic allocation showed improvements for all services across the cell, whilst keeping streams synchronised despite increased user loading.

A two-step resource allocation procedure for LTE-based cognitive radio network

We consider the problem of resource allocation for the Third Generation Partnership Project (3GPP) long-term evolution (LTE) cognitive radio network (CRN). The CRN is made up of the licensed (primary) service stations which can share their spectrum resources with the unlicensed (secondary) stations. The objective is to provide wireless access to the secondary stations on a best effort basis without compromising the quality of service (QoS) for the primary stations. To accomplish this we employ a simple two-step procedure. In the first step the spectrum resources are allocated to primary stations to maximize the QoS for the primary users. In the second step the spare service capacity of the primary channels is distributed among the secondary stations to maximize the QoS of the secondary users. The proposed theoretical framework adheres closely with the LTE specification. The corresponding resource allocation algorithm does not involve additional network signaling over the wireless medium, and improves the overall QoS in the network. These advantages of the proposed approach for resource allocation make it ready for implementation in a real network.

LTE 시스템 채널 추정치의 후처리 기법 연구

The Long Term Evolution (LTE) system is designed to provide a high quality data service for fast moving mobile users. It is based on the Orthogonal Frequency Division Multiplexing (OFDM) and relies its channel estimation on the training samples which are systematically built within the transmitting data. Either a preamble or a lattice type is used for the distribution of training samples and the latter suits better for the multipath fading channel environment whose channel frequency response (CFR) fluctuates rapidly with time. In the lattice-type structure, the estimation of the CFR makes use of the least squares estimate (LSE) for each pilot samples, followed by an interpolation both in timeand in frequency-domain to fill up the channel estimates for subcarriers corresponding to data samples. All interpolation schemes should rely on the pilot estimates only, and thus, their performances are bounded by the quality of pilot estimates. However, the additive noise give rise to high fluctuation on the pilot estimates, especially in a communication environment with low signal-to-noise ratio. These high fluctuations could be monitored in the alternating high values of the first forward differences (FFD) between pilot estimates. In this paper, we analyzed statistically those FFD values and propose a postprocessing algorithm to suppress high fluctuations in the noisy pilot estimates. The proposed method is based on a localized adaptive moving-average filtering. The performance of the proposed technique is verified on a multipath environment suggested on a 3GPP LTE specification. It is shown that the mean-squared error (MSE) between the actual CFR and pilot estimates could be reduced up to 68% from the noisy pilot estimates.

다속신호처리 기법을 이용한 LTE 시스템 채널 추정기법 설계

The Long Term Evolution (LTE) system is based on the Orthogonal Frequency Division Multiplexing (OFDM) and relies its channel estimation on the lattice-type pilot samples in the multipath fading channel environment. The estimation of the channel frequency response (CFR) makes use of the least squares estimate (LSE) for each pilot samples, followed by an interpolation both in time- and in frequency-domain to fill up the channel estimates for subcarriers corresponding to data samples. Any interpolation scheme could be adopted for this purpose. Depending on the requirements of the target system, we may choose a simple linear interpolation or a sophisticated one. For any choice of an interpolation scheme, these is a trade-off between estimation accuracy and numerical cost. For those wireless communication systems based on the OFDM and the preamble-type pilot structure, the DFT-based channel estimation and its variants have been successfully. Yet, it may not be suitable for the lattice-type pilot structure, since the pilot samples are not sufficient to provide an accurate estimate and it is known to be sensitive to the location as well as the length of the time-domain window. In this paper, we propose a simple interpolated based on the upsampling mechanism in the multirate signal processing. The proposed method provides an excellent alternative to the DFT-based methods in terms of numerical cost and accuracy. The performance of the proposed technique is verified on a multipath environment suggested on a 3GPP LTE specification.