In order to satisfy the requirements of future IMT-Advanced mobile systems, the concept of spectrum aggregation is introduced by 3GPP in its new LTE-Advanced (LTE Rel. 10) standards. While spectrum aggregation allows aggregation of carrier components (CCs) dispersed within and across different bands (intra/inter-band) as well as combination of CCs having different bandwidths, spectrum aggregation is expected to provide a powerful boost to the user throughput in LTE-Advanced (LTE-A). However, introduction of spectrum aggregation or carrier aggregation (CA) as referred to in LTE Rel. 10, has required some changes from the baseline LTE Rel. 8 although each CC in LTE-A remains backward compatible with LTE Rel. 8. This article provides a review of spectrum aggregation techniques, followed by requirements on radio resource management (RRM) functionality in support of CA. On-going research on the different RRM aspects and algorithms to support CA in LTE-Advanced are surveyed. Technical challenges for future research on aggregation in LTE-Advanced systems are also outlined.

A Survey of Radio Resource Management for Spectrum Aggregation in LTE-Advanced

Carrier aggregation (CA) is one of the promising techniques for the further advancements of the third-generation (3G) long-term evolution (LTE) system, referred to as LTE-Advanced. When CA is applied, a well-designed carrier scheduling (CS) scheme is essential to the LTE-Advanced system. Joint user scheduling (JUS) and separated random user scheduling (SRUS) are two straightforward CS schemes. JUS is optimal in performance but with very high complexity, whereas SRUS is contrary. Consequently, the authors propose a novel CS scheme, termed as ‘separated burst-level scheduling’ (SBLS). In SBLS, the connected component carrier (CC) of one user can be changed in burst level, whereas in SRUS, it is fixed. Meanwhile, SBLS limits the users to receive from only one of the CCs simultaneously, which is the same as that in SRUS. In this way, SBLS is expected to achieve higher resource utilisation than SRUS but with acceptable complexity increase. There are two factors that are important to the performance of SBLS, namely the dispatching granularity and the dispatching policy. The authors' analysis is verified by system-level simulations. The simulation results also show that the resultant performance gain of SBLS over SRUS is notable and increasing dispatching granularity will quickly deteriorate the performance of SBLS.

Performance analysis on carrier scheduling schemes in the long-term evolution-advanced system with carrier aggregation

In order to meet the requirement of wider bandwidth in IMT-Advanced, carrier aggregation (CA) is introduced by 3GPP to support bandwidth up to 100MHz in its LTE-Advanced standards. An LTE Rel.10 UE can aggregate up to 5 component carriers (CCs) simultaneously, but may be assigned only part of the total available CCs depending on its capability or traffic load. Thus, a proper CC selection method is necessary. First, two traditional CC selection methods respectively named Random and Round Robin CC selection are investigated, which can well balance the load across different CCs. However, neither of them is suitable for non-continuous CA scenarios through our analysis. To solve this problem, an improved CC selection method for non-continuous CA is proposed in this paper. Simulation results demonstrate that the proposed method outperforms both of the traditional ones.

Improved Component Carrier Selection Method for Non-Continuous Carrier Aggregation in LTE-Advanced Systems

Long Term Evolution-Advanced (LTE-Advanced) provides considerably higher data rates than even early releases of LTE. One key enhancement feature is bandwidth extension by the use of multicarrier technology to support deployment bandwidth up to 100 MHz. In order to achieve up to 1 Gb/s peak data rate in IMT-Advanced mobile systems, carrier aggregation technology is introduced by the 3GPP to support very-high-data-rate transmissions over wide frequency bandwidths (e.g., up to 100 MHz) in its new LTE-Advanced standards. The carrier aggregation (CA) technology allows scalable expansion of effective bandwidth provided to a user terminal through simultaneous utilization of radio resources across multiple carriers. The CA in LTE-Advanced is designed to support aggregation of a variety of different arrangements of component carriers (CCs), including CCs of the same or different bandwidths, contiguous or non- contiguous CCs in the same frequency band, and CCs in different frequency bands. The CA is supported by both formats of LTE, specifically the frequency Division Duplex (FDD) and Time Division Duplex (TDD) variants. This guarantees that both FDD LTE and TDD LTE are able to meet the high data throughput requirements placed upon them. This paper provides an outline of carrier aggregation including aggregation structure, deployment scenarios, implementation, main design features and backward compatibility with legacy LTE systems.

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Carrier aggregation in Long Term Evolution-Advanced

In the further advancements for the third generation (3G) long-term evolution (LTE) system, i.e. the LTE-Advanced system, carrier aggregation (CA) is applied to support wide system bandwidth and ensure backward compatibility. In this paper, two traffic load balance methods are proposed to improve the performance of the independent carrier scheduling (ICS) scheme in CA based LTE-Advanced system with time-variant user population. One is to utilize advanced user allocation rules. The other is a novel method which couples the component carriers (CCs) together in the scenario that the CCs are in the different working states. Our simulation results show that well-designed user allocation rules can achieve better traffic load balance across the CCs than the simplest random allocation rule. Moreover, the CC coupling method can make the ICS scheme achieve optimal performance as the joint carrier scheduling (JCS) scheme, irrespective of the traffic intensity and the used user allocation rule. However, using better user allocation rule can reduce the CC coupling time for the ICS scheme, which is essential to the practicality of ICS.

Traffic load balance methods in the LTE-Advanced system with carrier aggregation

Carrier aggregation (CA) is a good solution for third-generation (3G) Long Term Evolution-Advanced (LTE-A) systems to fulfil the system bandwidth (BW) extension requirements and also ensure the backwards compatibility towards 3G LTE In this paper, we compare the quality of service (QoS) performances of two different multi-user scheduling schemes in CA based LTE-A systems, ie separated random user scheduling (SRUS) and joint user scheduling (JUS) The former is simpler but less efficient while the latter is optimal but with higher signalling overhead Moreover, only one single component carrier (CC) is needed to access for user equipment (UE) in the case of SRUS while all the CCs have to be connected in the case of JUS Simulation results show that the SRUS scheme is feasible and only little performance loss in continuous and heavy traffic load scenarios with full or Poisson-based finite buffer traffic input

QoS performance analysis on carrier aggregation based LTE-A systems

In wireless networks, determining the error bit positions within a packet at the receiver can improve the wireless retransmission efficiency in wireless communications. In this paper, we propose an Error Position Estimating Coding (EPEC) scheme based on Error Estimating Coding (EEC). Specifically, we divide data bits into several groups and indicate the group number individually to implement error position estimating at the receiver. Moreover, we encodes Cyclic Redundancy Check (CRC) with the initial EEC to reduce the leak probability of error position detection. Experimental results show that the error position estimation accuracy is nearly 100% when bit error rate (BER) is lower than 10−3. And the bandwidth for data retransmission saved by EPEC is up to 87% on average. In addition, the miss rate of EPEC is almost 0% while EEC is about 0.06%.

Yumei Wang

Papers

QoS performance analysis on carrier aggregation based LTE-A systems

EPEC: An Error Position Estimating Coding scheme in wireless networks

ePec-LDPC HARQ: An LDPC HARQ Scheme with Targeted Retransmission