24-07-2012, 05:04 PM
LTE-ADVANCED: NEXT-GENERATION WIRELESS BROADBAND TECHNOLOGY
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ABSTRACT
LTE Release 8 is one of the primary broadband technologies based on OFDM, which is currently being commercialized. LTE Release 8, which is mainly deployed in a macro/microcell layout, provides improved system capacity and
coverage, high peak data rates, low latency, reduced operating costs, multi-antenna support, flexible bandwidth operation and seamless integration with existing systems. LTE-Advanced (also known as LTE Release 10) significantly enhances the existing LTE Release 8 and supports much higher peak rates, higher throughput
and coverage, and lower latencies, resulting in a better user experience. Additionally, LTE Release 10 will support heterogeneous deployments where low-power nodes comprising picocells, femtocells, relays, remote radio heads, and so on are placed in a macrocell layout. The LTE-Advanced features enable one to meet or exceed IMT-Advanced requirements. It may also be noted that LTE Release 9 provides some minor enhancement to LTE Release 8 with respect to the air interface, and includes features like dual-layer beamforming and time -difference-of-arrival-based location techniques. In this article an overview of the techniques being considered for LTE Release 10 (aka LTEAdvanced) is discussed. This includes bandwidth extension via carrier aggregation to support deployment bandwidths up to 100 MHz, downlink spatial multiplexing including single-cell
multi-user multiple-input multiple-output transmission and coordinated multi point transmission, uplink spatial multiplexing including extension to four-layer MIMO, and heterogeneous networks with emphasis on Type 1 and Type 2 relays. Finally, the performance of LTEAdvanced using IMT-A scenarios is presented and compared against IMT-A targets for full buffer and bursty traffic model.
INTRODUCTION
Universal Mobile Telecommunications System (UMTS) Long Term Evolution (LTE) Release 8 provides high peak data rates of 300 Mb/s on the downlink and 75 Mb/s on the uplink for a 20 MHz bandwidth, and allows flexible bandwidth operation of up to 20 MHz. Currently, enhancements are being studied to provide substantial improvements to LTE Release 8, allowing it to meet or exceed International Mobile Telecommunications- Advanced (IMT-A) requirements [1].
These enhancements are being considered as part of LTE-Advanced (LTE-A, also known as LTE Release 10), which includes carrier aggregation, advanced uplink (UL) and downlink (DL) spatial multiplexing, DL coordinated multipoint (CoMP)
transmission, and heterogeneous networks with special emphasis on Type 1 and Type 2 relays.
This article provides an overview of the technologies being considered for LTE-A. This article is organized as follows. In the next section an overview of the LTE Release 8 physical layer (PHY) is provided. This is followed by an overview of evolved UMTS terrestrial radio access (E-UTRA) LTE-A requirements. In the following section a discussion on carrier aggregation is provided. We then provide an overview of DL and UL spatial multiplexing and fundamentals of DL CoMP design. We introduce the concept of heterogeneous networks, withy an emphasis on LTE relays. We compare the performance of LTE Release 8 and LTE-A in the context of IMT-A requirements. Finally, conclusions are drawn in the last section.
LTE is the result of the standardization work done by the 3GPP to achieve a new high speed radio access in the mobile communications frame. It was introduced in the Release 8 in 2008. In 2010 the Release 9 has come to provide some enhancements to LTE and in 2011 Release 10 will bring LTE-Advanced, which will expand the limits and features of Release 8 to meet the requirements of the IMT-Advanced of ITU-R for the fourth generation of mobile technologies (4G), and the future operator and end user’s requirements. LTE-Advanced terminals have to be compatible with LTE-Release8 networks and vice versa, LTE-Release 8 terminals have to be compatible with LTE-Advanced networks. The key measure of LTE is the ability to provide very high bit rates. In addition, it provides high spectral efficiency, very low latency and support of variable bandwidth. Some of the LTE new features are:
OFDMA, a multi-user version of the modulation scheme called (Orthogonal Frequency-Division Multiplexing) in the downlink. This gives robustness against multipath interference and connects with some advanced techniques also used like MIMO and frequency domain channel‐dependent scheduling.
Single-Carrier FDMA with Dynamic Bandwidth in the uplink. SC-FDMA has lower peak-to-average power ratio (PAPR) which is a major improvement for the user equipment (UE), as it improves the transmission power efficiency.
Multiple antenna solutions. MIMO (Multiple Input Multiple Output) is probably the most important feature of LTE for improving the data bit rates and the spectral efficiency. It consists on the use of multiple antennas in both the receiver and the transmitter in order to use the multipath effects, which reduces the interference and leads to high transmission rates. MIMO works by dividing the data flow into multiple unique flows, and transmits them in the same radio channel at the same time. They will be merged using an algorithm or special signal processing.
Very low latency due to a short setup time and small transfer delays. This is a basic feature as many applications, especially the ones related to voice and video transfer, rely on low latency times.
LTE can support variable bandwidths, in the range between 1.4 and 20MHz.
LTE-Advanced extends the features of LTE in order to exceed or at least meet the IMT-Advanced requirements. It should be a real broadband wireless network that behaves as an advanced fixed network like FTTH (Fiber To The Home) but with better quality of service. It also must fulfil operators’ demands like a reduced cost (per Mbit transmitted), compatibility with all 3GPP previous systems and a better service providing in terms of homogeneity, constant quality of the connection and smaller latency. Here we list some of the LTE-Advanced proposals to achieve the goals of this standard:
Support of asymmetrical bandwidths and larger bandwidth (maximum of 100MHz). In LTE (release 8), the bandwidth could have different sizes but had to be the same in the downlink and in the uplink. In LTE-Advanced (Release 10) bandwidths can be different because due to actual demand in mobile networks, the traffic from the station to the user is bigger than the one from the user to the station. And they can be as asymmetric as they want within the limit of the 100 MHz LTE-Advanced provides. The sum of both bandwidths (downlink + uplink) cannot exceed 100 MHz. Carrier aggregation to achieve wider bandwidth is a key factor as well as the support of spectrum aggregation, to achieve higher bandwidth transmissions.
Enhanced multi-antenna transmission techniques. LTE introduced MIMO in the data transmission and LTE-Advanced the MIMO scheme has to be extended to gain spectrum efficiency (which is proportional to the number of antennas used), cell edge performance and average data rates. LTE-Advanced considers a configuration 8x8 in the downlink and 4x4 in the uplink.
[attachment=28779]
ABSTRACT
LTE Release 8 is one of the primary broadband technologies based on OFDM, which is currently being commercialized. LTE Release 8, which is mainly deployed in a macro/microcell layout, provides improved system capacity and
coverage, high peak data rates, low latency, reduced operating costs, multi-antenna support, flexible bandwidth operation and seamless integration with existing systems. LTE-Advanced (also known as LTE Release 10) significantly enhances the existing LTE Release 8 and supports much higher peak rates, higher throughput
and coverage, and lower latencies, resulting in a better user experience. Additionally, LTE Release 10 will support heterogeneous deployments where low-power nodes comprising picocells, femtocells, relays, remote radio heads, and so on are placed in a macrocell layout. The LTE-Advanced features enable one to meet or exceed IMT-Advanced requirements. It may also be noted that LTE Release 9 provides some minor enhancement to LTE Release 8 with respect to the air interface, and includes features like dual-layer beamforming and time -difference-of-arrival-based location techniques. In this article an overview of the techniques being considered for LTE Release 10 (aka LTEAdvanced) is discussed. This includes bandwidth extension via carrier aggregation to support deployment bandwidths up to 100 MHz, downlink spatial multiplexing including single-cell
multi-user multiple-input multiple-output transmission and coordinated multi point transmission, uplink spatial multiplexing including extension to four-layer MIMO, and heterogeneous networks with emphasis on Type 1 and Type 2 relays. Finally, the performance of LTEAdvanced using IMT-A scenarios is presented and compared against IMT-A targets for full buffer and bursty traffic model.
INTRODUCTION
Universal Mobile Telecommunications System (UMTS) Long Term Evolution (LTE) Release 8 provides high peak data rates of 300 Mb/s on the downlink and 75 Mb/s on the uplink for a 20 MHz bandwidth, and allows flexible bandwidth operation of up to 20 MHz. Currently, enhancements are being studied to provide substantial improvements to LTE Release 8, allowing it to meet or exceed International Mobile Telecommunications- Advanced (IMT-A) requirements [1].
These enhancements are being considered as part of LTE-Advanced (LTE-A, also known as LTE Release 10), which includes carrier aggregation, advanced uplink (UL) and downlink (DL) spatial multiplexing, DL coordinated multipoint (CoMP)
transmission, and heterogeneous networks with special emphasis on Type 1 and Type 2 relays.
This article provides an overview of the technologies being considered for LTE-A. This article is organized as follows. In the next section an overview of the LTE Release 8 physical layer (PHY) is provided. This is followed by an overview of evolved UMTS terrestrial radio access (E-UTRA) LTE-A requirements. In the following section a discussion on carrier aggregation is provided. We then provide an overview of DL and UL spatial multiplexing and fundamentals of DL CoMP design. We introduce the concept of heterogeneous networks, withy an emphasis on LTE relays. We compare the performance of LTE Release 8 and LTE-A in the context of IMT-A requirements. Finally, conclusions are drawn in the last section.
LTE is the result of the standardization work done by the 3GPP to achieve a new high speed radio access in the mobile communications frame. It was introduced in the Release 8 in 2008. In 2010 the Release 9 has come to provide some enhancements to LTE and in 2011 Release 10 will bring LTE-Advanced, which will expand the limits and features of Release 8 to meet the requirements of the IMT-Advanced of ITU-R for the fourth generation of mobile technologies (4G), and the future operator and end user’s requirements. LTE-Advanced terminals have to be compatible with LTE-Release8 networks and vice versa, LTE-Release 8 terminals have to be compatible with LTE-Advanced networks. The key measure of LTE is the ability to provide very high bit rates. In addition, it provides high spectral efficiency, very low latency and support of variable bandwidth. Some of the LTE new features are:
OFDMA, a multi-user version of the modulation scheme called (Orthogonal Frequency-Division Multiplexing) in the downlink. This gives robustness against multipath interference and connects with some advanced techniques also used like MIMO and frequency domain channel‐dependent scheduling.
Single-Carrier FDMA with Dynamic Bandwidth in the uplink. SC-FDMA has lower peak-to-average power ratio (PAPR) which is a major improvement for the user equipment (UE), as it improves the transmission power efficiency.
Multiple antenna solutions. MIMO (Multiple Input Multiple Output) is probably the most important feature of LTE for improving the data bit rates and the spectral efficiency. It consists on the use of multiple antennas in both the receiver and the transmitter in order to use the multipath effects, which reduces the interference and leads to high transmission rates. MIMO works by dividing the data flow into multiple unique flows, and transmits them in the same radio channel at the same time. They will be merged using an algorithm or special signal processing.
Very low latency due to a short setup time and small transfer delays. This is a basic feature as many applications, especially the ones related to voice and video transfer, rely on low latency times.
LTE can support variable bandwidths, in the range between 1.4 and 20MHz.
LTE-Advanced extends the features of LTE in order to exceed or at least meet the IMT-Advanced requirements. It should be a real broadband wireless network that behaves as an advanced fixed network like FTTH (Fiber To The Home) but with better quality of service. It also must fulfil operators’ demands like a reduced cost (per Mbit transmitted), compatibility with all 3GPP previous systems and a better service providing in terms of homogeneity, constant quality of the connection and smaller latency. Here we list some of the LTE-Advanced proposals to achieve the goals of this standard:
Support of asymmetrical bandwidths and larger bandwidth (maximum of 100MHz). In LTE (release 8), the bandwidth could have different sizes but had to be the same in the downlink and in the uplink. In LTE-Advanced (Release 10) bandwidths can be different because due to actual demand in mobile networks, the traffic from the station to the user is bigger than the one from the user to the station. And they can be as asymmetric as they want within the limit of the 100 MHz LTE-Advanced provides. The sum of both bandwidths (downlink + uplink) cannot exceed 100 MHz. Carrier aggregation to achieve wider bandwidth is a key factor as well as the support of spectrum aggregation, to achieve higher bandwidth transmissions.
Enhanced multi-antenna transmission techniques. LTE introduced MIMO in the data transmission and LTE-Advanced the MIMO scheme has to be extended to gain spectrum efficiency (which is proportional to the number of antennas used), cell edge performance and average data rates. LTE-Advanced considers a configuration 8x8 in the downlink and 4x4 in the uplink.