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Abstract
This paper presents a brief overview about the emerging characteristics of LTE-Advanced towards its recognition as an IMT-Advanced technology. The fundamental knowledge about LTE-Advanced is provided and ways to improve the bandwidth and the use of MIMO antennas of higher orders are discussed. These deployments will be based upon the existing structure of LTE release 8 and will be regarded as a 4G technology.
Keywords- LTE release 8, LTE-Advanced, IMT-Advanced, MIMO, 4G
1. Introduction
Long Term Evolution-Advanced (LTE-Advanced) is a Fourth Generation (4G) concept developed by the Third Generation Partnership Project (3GPP) for its deployment as an International Mobile Telecommunications-Advanced (IMT-Advanced) technology, monitored by the International Telecommunications Union for Radio communications (ITU-R). This forthcoming technology is a technological successor to LTE, which has currently established 51 network commitments across 21 countries [3].
LTE-Advanced will be superior to LTE in terms of higher order Multiple-in-Multiple-out (MIMO), typically 4x4 MIMO and beyond, high peak data rates about 1 Gbps on downlink and 500 Mbps on uplink [1] and more efficient spectrum utilization by incorporating more number of users. As an evolution of LTE, LTE-Advanced will be backward compatible with its predecessors and will use the spectrum utilized by LTE [1].
Apart from the above mentioned requirements, LTE-Advanced must satisfy the criteria required by IMT-Advanced in order to be recognized by the ITU-R as an IMT-Advanced technology.
2. Emerging characteristics for Recognition as IMT-Advanced
2.1 Improvisation of Bandwidth
The first release of LTE (known as LTE release 8) examined the variation of bandwidths ranging from 1.25 MHz to around 20 MHz required for spectrum allocation, which provides peak LTE data rates of 300 Mbps [1].
Figure 1: Carrier aggregation [1]
As discussed by the 3GPP, transmission bandwidths up to 100 MHz would be deployed in order to achieve very high data rates for LTE-Advanced, much higher than the ITU-R requirement of 60 MHz. Also, spectrum allocation must be kept in mind to deploy very high transmission bandwidths. Therefore, a technique known as carrier aggregation [1] can be used to combine multiple LTE component carriers (from LTE release 8) on the physical layer to provide the necessary bandwidth [1] as shown in figure 1. The LTE-Advanced equipment will be able to utilize the total aggregated bandwidth of 100 MHz, whereas each component carrier will appear as an LTE carrier for LTE terminals, i.e., typical allotment of 20 MHz to LTE terminals [1].
The conterminous spectrum of the order of 100 MHz may not be available at all times, hence, the aggregation of the non-conterminous component carriers can be done if the large contiguous spectrum is not present. The implementation of aggregation of the non-conterminous component carriers is a difficult task although supported by the basic specifications of the process [1]. For the LTE-Advanced terminals to receive the multiple component carriers, the presence of broadcasting and synchronization signals are mandatory on any one of the component carriers [1]. The high transmission bandwidths can also result in the provisions for more coverage for medium data rates.
The carrier aggregation discussed earlier is used in the layered Orthogonal Frequency Division Multiple Access (OFDMA) radio access technique for LTE-Advanced. This layered OFDMA radio access can achieve significantly higher requirements with respect to the system performance and capability parameters as compared to the radio access approach used in LTE release 8 [2]. The continuous spectrum allocation concept (used by layered OFDMA for LTE-Advanced) was adopted by the 3GPP Radio Access Working Group1, as the approach is backward compatible with the LTE release 8 user equipments and can be deployed with IP-functionality capabilities, low latency and low cost with the existing Radio Access Network (RAN) [2].
2.2 Use of higher order MIMO antennas
The MIMO technologies used for LTE constitute mainly of spatial multiplexing and beam-forming. Since LTE-Advanced is backward compatible with LTE, the two main components play a major role in the yet to be released LTE-Advanced. The present LTE architecture supports 4x4 MIMO antennas for transmitting reference signals in the downlink.
LTE-Advanced requires a high Signal to Noise Ratio (SNR). Spatial multiplexing can provide a high SNR due to which it is regarded to be a part of LTE-Advanced architecture on the uplink [1]. Alternate configurations rather then 4x4 MIMO for downlink transmission at the antennas can be used. Higher order antennas such as 8x8 MIMO for downlink and 4x8 MIMO for uplink can also be used and are major considerations while establishing the structure for LTE-Advanced. These configurations improve SNR in Wide Area Networks (WAN) as required by the advanced technology [1].
3. Conclusion
This paper has discussed the techniques used for the radio access technology and ways to improvise the bandwidth to be used by both LTE-Advanced terminals and LTE release 8 terminals. Also, the use of higher order MIMO antennas will help in increasing the spectral efficiency, reducing interference and providing a high SNR at low cost, low latency and by providing full IP-architecture deployment with increased system performance.
References
[1] Stefan Parkvall, Erik Dahlman, Anders Furuskär, Ylva Jading, Magnus Olsson, Stefan Wänstedt, Kambiz Zangi,
“LTE-Advanced – Evolving LTE towards IMT-Advanced”, Ericsson Research;
http://www.ericsson.com/technology/research_papers/wireless_access/doc/VTC08F_jading.pdf
[2] Takeda, K.; Nagata, S.; Kishiyama, Y.; Tanno, M.; Higuchi, K.; Sawahashi, M., “Investigation on Optimum Radio
Parameter Design in Layered OFDMA for LTE-Advanced”,Vehicular Technology Conference, 2009
[3] Global Mobile Subscriber Association (GSA), “World Map of 51 LTE network commitments”, December 10, 2009
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