Key Technologies LTE And Lte Advanced Information Technology Essay

LTE is pre-4G technology which provides high data speed, volume, and more coverage area. Besides that, LTE can decease the delay process; the operational cost of the system as well as evolution of 4G in the future is maintained. This paper will introduce the difference between LTE and LTE advanced, LTE performance as well as critical technologies of LTE system.

LTE (Long Term Evolution) is the latest standard in the moblile network technology tree that previously realized the GSM/EDGE/ and UMTS/HSxPA network technologies. It is a project standardized by the 3rd Generation Partnership Project (3GPP) as a major enhancement to 4G 3GPP Long Term Evolution (LTE) standard. LTE being described as 3.9G technology since the first release LTE does not fully meet with the IMT Advanced 4G requirements as defined by the International Telecommunication Union (ITU) such as peak data rates up to 1Gbit/s. Hence, ITU has offered the submission of candidate Radio Interface Technologies (RITs) following their requirement.[1] the LTE Advanced is reach and surpass the ITU requirement. **LTE Advanced is the pre-4G standard that designed to increase the capacity and speed of mobile telephone network.** LTE Advanced is backwards compatible with LTE and uses the same frequency bandwidth, while LTE is not backwards compatible with 3G systems.

LTE and LTE Advance is more advantage than other mobile network technology because LTE improves capacity, coverage and ensures user fairness. Besides that, it have more ability to leverage advanced topology networks. And it optimized heterogeneous network with a mix of macros with low power modes such as picocells, femtocells and new relay nodes. Furthermore, it introduces multicarrier to be able to leverage ultra wide bandwidth, up to 100MHz of spectrum supporting very high data rates.

Nowadays, LTE advanced is more nearly achieve the target of ITU, below are the comparision between LTE and LTE advanced: [2]

Peak data rates: downlink – 1Gbps; uplink – 500Mbps.

Spectrum efficiency: 3 times greater than LTE

Peak spectrum efficiency: downlink – 30bps/hz; uplink – 15bps/hz

Spectrum use: the ability to support scalable bandwidth use and spectrum aggregation where non-contiguous spectrum needs to be used

Latency: from Idle to Connected in less than 50ms and then shorter than 5ms one way for individual packet teransmission.

Cell edge user throughput to be twice that of LTE

Average user throughput to be 3 times that of LTE

Mobility: same as that in LTE

Compatibility: LTE advanced shall be capable of interworking with LTE and 3GPP legacy systems.

Channel characterization

The main principles of LTE physical layer design, which lead to new Radio Resource Management (RRM) opportunities that are significantly different from the ones applied in GSM and WCDMA/HSPA. [3]

Downlink: OFDMA

LTE downlink modulation is based on multicarrier transmission of subcarrier signals, ie. Orthogonal Frequency Division Multiplexing (OFDM). [3] As long as the channel delay spread remains within the CP, the subcarriers are orthogonal. In the transmitter, the subcarrier signals are generated in the frequency domain by an Inverse FFT. In the receiver, after discarding the CP, the FFT is used to recover the transmitted signals. In LTE, the data of different users is multiplexed in the frequency domain, and accordingly the downlink is characterized as OFDMA.

LTE uses OFDMA as downlink multiple access plan as figure 1.

Figure 1: LTE Downlink Multiple Access

Uplink: SC-FDMA

LTE uplink is designed to be in-cell orthogonal. This is contrary to the WCDMA/HSPA uplink, which is non-orthogonal and targets at randomizing the intracell interference by long scrambling sequences. Non-orthogonal multiple access is in theory superior to orthogonal, if ideal multiuser detection is used. However, channel estimation imperfections limit the multiuser efficiency, especially at high load and high SNR. Another important feature underlying the selection of the LTE uplink transmission technique is the need to sacrifice power and symbol resources for the channel estimation. Spreading the transmission over the whole bandwidth is not sensible for transmitters with limited power resources-the wider the bandwidth, the larger the overhead needed for the pilot signals. Frequency Division Multiple Access (FDMA) is the basis uplink user multiplexing together with the bandwidth flexibility target of LTE. To keep the peak-to-average power ratio small, a Single Carrier transmission format was adopted. In this respect, LTE uplink returns to the GSM principle of utilizing power efficient modulation, which was partially sacrificed in uplink HSPA. To solve the equalization problems, a Single Carrier FDMA (SC-FDMA) transmission format with a cyclic prefix was adopted. This allows for a power efficient modulation, yet equalizable in the frequency domain, SC-FDMA can be interpreted as DFT-spread OFDMA.

LTE uses DFT-SOFDM (SC-FDMA) as uplink multiple access plan.

Figure 2: LTE Uplink Multiple Access

System performance

LTE baseline performance is the cumulative throughput experienced in a cellular network serving multiple users per cell. The baseline here means that moderate antenna configurations are used at the base station sites, and the UE capability includes 2 receive antennas. This type of analysis also reveals fairness among the served UEs. In cellular networks, cell edge performance is often valued because it is the most challenging regime of signal processing and signaling, and the region where the interference limitation of cellular networks is most strongly felt. For a uniform geographical user distribution, relatively large number of users gets served at cell edge areas.

Key technologies

MIMO( Multi input Multi output)

The DL MIMO transmission schemes already supported in LTE Release 8 include transmit-diversity and open-loop and closed-loop spatial multiplexing with up to 4 layers. However, the performance of the multi-user MIMO (MU-MIMO) scheme is limited by coarse quantization and the lack of support for cross-talk suppression at the UE. Fortunately, LTE releases 9 and 10 is going to fix the MU-MIMO performance. It will improve the single-cell DL MU-MIMO support, extend to 8-layer DL spatial multiplexing, extend to 4-layer UL spatial multiplexing and add DL CoMP support. How it going to improve the single cell DL MU-MIMO support? First, in LTE have 2 layers of orthogonal UE specific reference signal have been introduced. This enables an eNB to transmit 2 layers of data to a UE set using spatial multiplexing in a closed-loop mode by constructing antenna weights using channel reciprocity. Additionally, this enables an eNB to transmit 2 layers of data to 2 UE sets using the same time-frequency resource in MU-MIMO fashion. Swithcing between single and dual-layer transmission to a single UE set, as well as between SU-MIMO and MU-MIMO is supported in a dynamic fashion. The control signaling overhead for supporting dynamic and transparent MU-MIMO transmission is small because UE is not explicitly informed of the presence of co-scheduled UE, for the purposes of feedback or demodualation. The 2 layers of UE-specific reference signals are overlaid on top of each other and a UE, after subtracting out its channel estimate, may estimate a covariance matrix representing the combined interference from a co-scheduled UE and outer cell transmissions. This feature can be used by a receiver to significantly suppress the interference due to MU-MIMO. The MU-MIMO enhancements in LTE release 9 provide substantial gain in sector throughput when the eNB is able to form transmit beams using reciprocity-based techniques. Note that with channel reciprocity based MU-MIMO, there is no restriction based MU-MIMO, there is no restriction on the number of transmit antennas that can be employed at the eNB. In addition, up to 4 layers of quasi-orthogonal UE-specific reference signals is available for MU-MIMO enabling co-scheduling of up to 4 UE sets in the same time-frequency resource.

[4] LTE-next generation technology.pdf

MIMO enhancement

LTE advance improve MIMO transmission. So, the gain for additional diversity becomes smaller. Anyway not always wanted e.g. frequency selective scheduling. Besides, gain from spatial multiplexing only is questionable. It will limit to hotspot and indoor environment (small cells, scattered propagation environment, very low user mobility) and the only way to achieve the very high peak data rates. The Spatial multiplexing in general needs high SNR regions. It will use of beam forming combined with spatial multiplexing within different beams could be most beneficial. Downlink MIMO transmission need 4UE receive antennas and 4×4 MIMO become baseline. Then, downlink peak data rates achieved by the use of 8×8 MIMO ( reference signals for 8 antennas required) For Uplink MIMO transmission, it need 2 UE transmit antennas and 2×2 MIMO could become baseline. And uplink peak data rate, but also coverage and capacity.

4G Wireless Technology in Car

If vehicle can applies LTE wireless technology car solution concept, consumer would be able to access network and cloud-based applications, putting on-demand entertainment, infotainment, diagnostics, and navigation. [5] Engineer in Russia carried out experimental investigation will car speed is 140km/h. The interactive system to send and receive signals works with data rates of 10Mbps.

Though this implementation, this will enabled ultra-hign bandwidth technology,

[5] Using 4G wireless in car, Jegor Mosyagin

Conclusion

The LTE technology to radically bring the 3G networks to a new 4G performance era. Through the key technologies above, we are more understood and know how the LTE technology is important in our life now. Hence, LTE are clearly be the future technology for the wide area mobile data coverage in dense traffic areas globally. LTE advanced reaches the target set for IMT-advanced [3],[9] in wide area evaluation scenarios. New releases of LTE, including technology components such as uplink MIMO and carrier aggregation, will improve LTE performance in local area scenarios, and factually realize 1Gbit/s peak rate, often seen as a rate characteristic of 4G systems.

[1] http://en.wikipedia.org/wiki/LTE_Advanced

[2] (from— Radio-Electronics.com/info/cellulartelecomms./4g/3gpp-imt-lte-advacned-tutorial.php)

[3] intro LTE 14.9.10

[9]ITU-R, Requirements related to technical performance for IMT-advanced radio interface(s), Report M.2134 (2008).