Thursday, November 28, 2019

LTE Networks Essay Example

LTE Networks Essay LTE Networks Name: Institution: LTE Networks We will write a custom essay sample on LTE Networks specifically for you for only $16.38 $13.9/page Order now We will write a custom essay sample on LTE Networks specifically for you FOR ONLY $16.38 $13.9/page Hire Writer We will write a custom essay sample on LTE Networks specifically for you FOR ONLY $16.38 $13.9/page Hire Writer 4G is the new generation of wireless networks that has evolved from the third generation of mobile broadband communication. It is based on integrating terminals, networks and applications to fulfill increased user demand. 4G comprises LTE technology, HSPA+ and WiMax technologies. It is a general term coined by the ITU due to the advancements of the respective technologies relative to the original 3G networks. LTE systems have been designed to correct the numerous flaws related to 3G systems. The LTE systems have also been targeted to provide new services for instance; HD Video streaming and high quality voice communication. A term used to describe 4G technology is MAGIC. Mobile multimedia, Anytime anywhere, Global mobility support, Integrated wireless solutions and Customized personal service. LTE mobile networks are expected to provide high usability, global coverage, and easier broadband connectivity. This will make it easier for Telecom companies to expand coverage and consumption to areas previously not covered by 3G networks. High network capacity and low cost user-oriented services are also expected with the rolling out of LTE services. 4G communications are based on the Open Wireless Architecture (OWA). This will ensure that a single terminal can seamlessly connect to local high-speed wireless systems. For instance, when in homes, airports or shopping malls, the terminal can switch to present wireless LAN networks. When the user moves to a mobile zone i.e. a highway, the terminal can automatically switch to wireless mobile networks e.g. WCDMA or GPRS. Implementation of high performance 4G broadband necessitates use of multiple antennas, at the base station and subscriber module. Multiple antenna technology enables high capacities suited for multimedia applications e.g. streaming videos. These technologies also increase range and reliability of such networks considerably. OFDM is preferred to single carrier solutions in implementation of LTE networks. This is due to lower complexity of equalizers for high delay spread channels. A broadband signal is broken down into several narrow band carriers (tones). Each carrier is more robust to multi-path propagation. A cyclic prefix is added to maintain orthogonality within the tones. The prefix usually has a length greater than the expected delay spread. With proper coding and interleaving across frequencies, multi-path is transformed into an OFDM system advantage. This is by yielding frequency diversity. OFDM can be efficiently implemented by use of Fast Fourier Transform (FFTs) algorithms at both the transmitter and receiver. At the receiver, FFT algorithms reduce the channel response to a multiplicative constant, on a tone-by-tone basis. With multiple input and multiple output (MIMO), the channel response becomes a matrix. As each tone can be independently equalized, the complexity of space-time equalizers is entirely avoided. Multi-path is maintained as an advantage for a MIMO-OFDM system. This is because frequency selectivity caused by multi-path significantly improves the rank distribution of the channel matrices across frequency tones. Therefore, capacity is increased to BTS-on-a-chip or System-in-Package. Background Orthogonal Frequency Division Multiplexing (OFDM) has become a popular technique for transmission of signals over wireless channels. It has been implemented in various ways for instance; digital audio broadcasting (DAB), digital video broadcasting( DVB-T), the IEEE 802.11a, a local area network (LAN) standard and the IEEE 802.16a, a metropolitan network (MAN) standard. OFDM is also being implemented for dedicated short-range communications (DSRC). It will facilitate roadside to vehicle communications as a potential candidate for fourth generation (4G) wireless systems. The man goal in development of next-generation wireless communication systems is increasing bit-rate (link throughput) as well as network capacity. OFDM translates a frequency-selective channel into a parallel collection of frequency flat sub channels. When knowledge of a channel is available at the transmitter, the OFDM transmitter can adapt its signaling methodology to meet the channel. Since OFDM utilizes a large set of narrowly spaced sub-channels, these adaptive strategies can approach the ideal water pouring capacity of a frequency-selective channel. This is achieved by use of adaptive bit loading technologies. Here, different sized signal constellations are transmitted onto the sub-carriers. All MIMO-OFDM receivers must perform time synchronization; frequency offset estimation and correction and finally, parameter estimation. Generally, this is carried out by use of a preamble composed of several training sequences. Important improvements in throughput can be achieved when multiple antennas are implemented at both the transmitter and receiver side, especially in a rich scattering environment. This has been shown for wireless communication links in flat-fading as well as frequency-selective fading channels, multiple-transmit, multiple-receive antenna, i.e. MIMO. For portrayal purposes, the techniques can be split into two groups: space-time coding (STC) AND space division multiplexing (SDM).STC improves the performance of the communication system by coding over the different transmitter branches. However, SDM achieves a higher throughput by transmitting independent data streams on the different transmit branches and at the same carrier frequency. A potential application of the MIMO principle is the next generation Wireless-LAN technology. The current WLAN standards are IEEE 802.11a and IEEE 802.11g. These standards are based on orthogonal frequency division multiplexing (OFDM). A potential high data rate extension of these standards could be based on MIMO. This leads to the promising combination of the data rate enhancement of SDM and the high spectral efficiency and robustness against frequency-selective fading and narrowband interference of OFDM. Wireless LAN systems have various advantages. One is that they are mainly deployed in indoor environments. Such environments are typically characterized by a richly scattered multi-path Implementation Preamble W-LAN is a packet-switched system with a random access protocol. This means that a receiver possesses no prior knowledge about packet-arrival times. The random nature of the arrival times as well as the high data rates necessitate the synchronization to be completed shortly after the start of the reception of a packet. To enable ‘quick’ synchronization, the data packet is normally preceded with a known sequence known as ‘the preamble’. The preamble is carefully designed to provide enough information for efficient packet detection, frequency offset estimation, symbol timing, and channel estimation. Once there is accurate knowledge of the MIMO channel elements, the MIMO processing can separate the signal components originating from the different transmit antennas. To approximate the MIMO channel, it is necessary that the sub-channels from the TX antennas be uniquely different from the RX antennas. For that to be achieved, the preambles on the different TX antennas must be orthogonal as well as shift-orthogonal, at least for the channel length. Time Synchronization: 1.) Frame Detection/Coarse Timing: The purpose for frame detection (FD) is to recognize the preamble in order to detect arrival of a packet. This preamble detection algorithm can also be used as a coarse timing (CT) algorithm. This is because it inherently provides a rough estimate of the packet’s starting point. Different data-aided FD algorithms have been proposed for OFDM. For instance, a simple MIMO extension of Schmidl’s timing offset algorithm was proposed. All these algorithms are based n the correlation between the repeated symbols constituting the preamble. 2.) Symbol Timing: The symbol timing in an OFDM system chooses where to place the start of the FFT window within the OFDM symbol. An OFDM system exhibits a guard interval (GI), making it somewhat robust against timing offsets. Non-optimal symbol timing will result into more ISI and inter-carrier interference (ICI) in delay spread environments. This will result in a decrease in performance. C. Frequency Synchronization It is necessary for the frequency synchronization to correct the frequency offset. This is due to the difference in oscillator frequencies at the transmitter and the receiver. D. Channel Estimation When time synchronization is performed at the receiver and after the received signals are corrected for the frequency offset, the channel can be estimated using the known training symbols within the preamble. When the timing is performed correctly, it can be known which received samples correspond to the timing part. Synchronization Tracking using Pilot Sub-carriers The processing of the preamble deals with the initial synchronization of the MIMO OFDM receiver. However, it is very likely that the frequency offset will vary during the packet’s reception. This makes solely initial frequency synchronization insufficient. Furthermore, the system will experience phase noise (PN) invoked by the combination of RF oscillator and the phase-locked loop (PLL). MIMO Detection Algorithms: Once a packet is recognized and the synchronization and channel estimation are done, the FFT begins retrieving the sub-carrier signals. MIMO detection is applied to these signals on a sub-carrier basis. In terms of spatial multiplexing, the MLD-based detection algorithm PAC SOMLD executes well. MIMO-OFMD Design Constraints The key channel characteristics influencing wireless broadband systems are channel dispersion, Rician K-factor, the Doppler effect, cross-polarization discrimination, antenna correlation and the condition number. Doppler Effect: The fixed wireless channel Doppler spectrum is significantly different from the mobile channel Doppler spectrum. For fixed wireless channels, it was found that the Doppler is in the 0.1-2 Hz frequency range. It also has close to exponential or rounded spectrum shape. However, for mobile wireless channels, the Doppler can be at around 100 Hz. It also has the Jake’s spectrum. Cross-Polarization Discrimination: The cross polarization discrimination (XPD) is defined as the ratio of the co-polarized average received power P2 to the cross-polarized average received power; P. XPD measures the separation between two transmission channels that use variant polarization orientations. The larger the XPD, the less energy is coupled between the cross-polarized channels. The XPD values were found to decrease with increasing distance. Antenna Correlation: Antenna correlation plays a paramount role in single-input multi-output (SIMO), multi-input single-output (MISO), and MIMO systems. If the complex correlation coefficient is relatively high (e.g. higher than 0.7), diversity and multiplexing gains can be significantly reduced (or completely diminished in the case of correlation of 1). Generally, it was discovered that the complex correlation coefficients are low, in the 0.1-0.5 range for properly selected base station and receiver antenna configurations. Condition Number: The condition number can be described as a ratio of the maximum and minimum Eigen values of the MIMO channel matrix. Large capacity gains from spatial multiplexing operations in MIMO wireless systems are possible. However, this is only when the statistical distribution of condition numbers mostly contains low values. LOS conditions often create undesirable MIMO matrix conditions (i.e. high condition numbers) that can be mitigated by use of dual-polarized antennas. For low BTS antennas, most propagation conditions are non-LOS with a considerable amount of scattering, in which case the multiplexing gains of MIMO systems are incredibly significant. Current obstacles Despite the aforementioned improvements over traditional 3G networks, 4G (specifically, LTE) faces numerous obstacles in its implementation today. First, its throughput though advantageous, put it at a huge disadvantage. The fast speeds provided risk network congestion due to growing popularity of mobile broadband. This is accentuated by the stagnant growth in capture of spectrum capacity. Modern wireless technologies also have performance limited to signal quality. Secondly, pricing has been used as a deterrent by Telecoms companies due to network capacity constraints. A gigabyte goes for around $10. Roaming also poses a problem to LTE technologies. This is because different countries use different LTE network bands. Consequently, mobile devices will most likely fall back to 3G, which is universal. Mobile broadband is mostly consumed by smartphones and tablets. LTE chips require significantly more power than their 3G counterparts do to run. Therefore, battery life comes up as a problem in early smartphones. This is accentuated by the fact that LTE phones consume data faster than their 3G counterparts do. Disadvantages LTE has several disadvantages. One, it is very expensive to set up. For starters, it requires a lot more base stations than their LMR equivalents (Land Mobile Radio). Secondly, LTE equipment is quite expensive to purchase and deploy. It requires a very skilled to implement. Such high costs force the Telecoms operators to pass them on to their customers. To use LTE networks, it is necessary for consumers to purchase new cell phones to make use of new network infrastructure. The LTE standard currently supports only packet switching, as it is an all-IP network. GSM, UMTS and CDMA networks however, circuit-switch their voice calls. This will force carriers to re-engineer their voice call networks, further driving up LTE adoption costs. The Future Current adoption of 4G is not as widespread as 3G. However, its future is already being seen by recent developments. In January 2013, the ITU approved two new standards; LTE-Advanced and Wireless MAN-Advanced. LTE-Advanced will succeed current LTE networks while WiMax networks will be followed by Wireless MAN-Advanced. LTE-Advanced has been designed to meet the current constraints facing LTE especially carrier capacity. It will not necessarily increase consumer speeds past LTE’s 100Mbps. However, it will improve the overall experience. LTE-Advanced will also feature four or more antennas in a mobile device. This will potentially boost speeds experienced and their reliability. However, current applications may not necessitate an increase in network speeds.

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