Model Railway Isolating Switches
INTERNAL CHALLENGES OF COVERAGE WiMAX TECHNOLOGY
INTERNAL CHALLENGES OF COVERAGE WiMAX TECHNOLOGY
Ramakrishna Dr.Hari
Professor, Department of CSE,
Chaitanya Bharathi Institute of Technology
Gandipet Hyderabad -500 075,
dr.hariramakrishna @ rediffmail.com
K. Ravi
Wizard. Professor
Department Computing
Alluri Institute of Management Sciences
K. Anil Kumar
Assoc. Professor
Department Computing
Alluri Institute of Management Sciences
ABSTRACT
Now the use of a mobile day is higher here than anywhere else in the world and mobile devices are used inside buildings, and network operators providing mobile coverage indoors with their service. In order to provide indoor coverage without having too much extra cost as additional cells, optimal network planning is done to help the coverage area using the network models.
In this paper we provide the concepts of what is covered coverage, difficulties in indoor coverage. How does WiFi and WiMAX technologies are used to improve the ability to provide indoor coverage. This work also includes architectural models and to provide better indoor coverage.
Keywords: Indoor coverage, domestic traffic of WiMAX, Wi-Fi modem, BTS, antenna,
1. INTRODUCTION
Mobile phone usage is higher here than anywhere else in the world and millions of subscribers in the demand for quality service wherever they go. Unfortunately for the operator, these subscribers are often the most difficult to fill places with a macro cellular wireless network, due to the unique topology, high-rise offices, subway stations, dense urban streets, shopping and entertainment areas with irregular hours occupied, hundreds of railway lines, and small apartments in buildings with large apartments.
Great coverage outside does not always mean perfect coverage inside. outdoor coverage (in the macro network) has steadily improved over time with more cell towers and better call rates declined. But in building coverage - in offices, commercial buildings and residences, can often be affected by things beyond the control of his company. Our cell phones and email addresses have become increasingly a way to stay connected no matter where we are. But building materials like concrete, concrete blocks, steel, brick and tinted glass, and construction sites in shaded areas, limit the penetration of the signals from cellular and PCS in place. Although changes in climate and environmental conditions external changes such foliage or the ground can affect the signal indoors.
Many WiMAX operators are at a crucial stage in the planning or the deployment of WiMAX networks. Your wait for spectrum licenses necessary to get the first delivery of Mobile WiMAX products, or to select a provider is by on or near the end. Finally, it is ready to start rolling out their networks and test in real environments, with paying subscribers in loaded networks.
Since operators have progressed through network planning or deployment, the hottest topics in the Radio Access Network (RAN) have become become airborne free and indoor coverage. As you start using the name of your network, providing high capacity density that the new devices and applications will require another key objective.
These are recurring themes for all wireless data technologies as the underlying physics they need to overcome to achieve good coverage and capacity are the same. WiMAX is no exception, despite the fact that multiple access techniques such as orthogonal frequency division (OFDMA) and Multiple Input Multiple Output (MIMO) improve coverage and capacity.
2. DIFFICULTIES IN THE COVERAGE OF INTERIOR
The combination of high capacity needs and access to extensive indoor network makes it a challenge to build a network of mobile broadband. This is not a unique challenge to WiMAX operators: Long Term Evolution (LTE) and Ultra Mobile Broadband (UMB), operators will face a very similar situation in due time. WiMAX indoor coverage adds a significant burden on existing network resources, such as loss of penetration due to the first wall in a building usually ranges from 10 to 20 dB.
To extend the range of coverage and improve indoor coverage, WiMAX changes its modulation scheme dynamically based on the location of the subscriber. But there is a steep price to pay, longer range and indoor results in reaching poor performance.
Outdoor devices located near the Base Transceiver Station (BTS) uses the most efficient modulation scheme, the quadrature amplitude modulation (QAM) it has a higher spectral efficiency. However, the majority of subscribers may be indoor locations or to the edge of the cell, where Quadrature Phase Shift Keying (QPSK) is used instead and has a lower spectral efficiency. The impact of modulation is substantial. When QPSK is used half the data rate can be as little as 20% capacity QAM maximum available with 5.6 as shown in Figure 1.
Figure 1: Impact of velocity modulation transmission in a WiMAX network
To make matters worse, internal subscribers are more likely to have longer sessions and more applications use bandwidth intensive, simply because they are more comfortable interior for data users. Over time, the largest number of users and mobile devices together with the wider use of high-performance applications, will further increase the overall need for network capacity, such as mobile devices use network resources to a greater extent due to antenna smaller and limited power.
WiMAX networks provide limited capacity and higher density of capacity will be needed due to the combination of high levels of indoor use, along with the increasing adoption of mobile devices, which usually can not use more efficient modulation in indoor places, and with the increase in user traffic levels.
A higher density of BTS is required to qualify for indoor coverage and capacity. The new cells added need to make efficient use of resources spectrum and network and actually have to include more traffic capacity in the same area. To achieve this, new network architectures are necessary and will be approached BTS to indoor places where subscribers are.
3. POSITION HIERARCHY ARCHITECTURE
Assume that the handheld devices carried by mobile users are able to receive broadcast signals heterogeneous wireless technologies such as networks WLAN and infrared. Figure 2 shows the architecture of the proposed internal hierarchical positioning service. For example, the mobile device is equipped with interfaces appropriate network ID to receive the signals transmitted by WLAN access points and infrared transmitters signal. The exact positions of the WLAN access points and the infrared signal transmitters have already been given. A program called the customer location, is installed on each mobile device.
Figure 2: Architecture of the proposed hierarchical positioning service interior
Identification signals are received, the location of mobile host client offers the signal strengths and the identifiers of all WLAN access points detected, or just the sender identification infrared signal to the server location. The server location will estimate the position of the mobile host, and then deliver the estimated position back to the client location. Then the location-based services corresponding to recover the estimated position to serve mobile users. The estimated positions are stored in the database, so the location of the server is able to trace the historical path of each mobile user movement. As a mobile host receives the identification signal from a transmitter infrared signal, the distance error of the estimated position is just a few inches several meters from the infrared signal transmitter. However, as the identification signal of a WLAN access point is received, the distance error of the estimated position is 10 to 100 meters from the WLAN access point.
Figure functional structure of the client and the server location instead: 3
The position information provided by the infrared signal transmitter is more accurate than those offered by WLAN access points, because the distance transmission of infrared positioning devices is much less than the WLAN access points. In general, WLAN access points can be deployed to cover the environment interior easily, but it is difficult for infrared signal transmitters. Therefore, the estimated positions by the location server are based on information about signal WLAN access points. Once the infrared signal is detected the position of the mobile host will be adjusted immediately to the position of the transmitter infrared signal, because the infrared technology is more accurate.
The proposed architecture is based on hierarchical position client / server.
The functional structure of the location of the server and client location is shown in Figure 3. The customer location out in the handheld module comprises signal collector, module location, and location-based service module. The collector module signal is responsible for detecting the positioning signals for heterogeneous wireless technologies. The management module is responsible for delivering the proceeds signal information as an indicator of received signal strength (RSSI) and infrared identification (IRID), the server location, and reception of the estimated position of the location of the server.
After receipt of the estimated position, the service module based on immediate location offers related services or actions for the mobile user. The location server is the placement of the engine and database. The positioning motor is responsible for estimating the position of the mobile user according to the signal information provided by the client location. Basically, the position can be estimated according to the RSSI values measured at least three access points.
Then the positioning engine makes the verification cross and the adjustment of the estimated position, according to the information signal heterogeneous wireless technologies, to improve accuracy. Another mission of positioning engine is to transmit the estimated position location module back to the location of the customer. The database is responsible for recording the estimated positions, so that the path of movement of each mobile user can be tracked and controlled.
4. And WiMAX indoor coverage
WiMAX promises ubiquitous connectivity in general, access devices and supports fixed and mobile broadband applications without sweat. However, Like other wireless broadband technologies in the market, the fundamental question remains for WiMAX in providing coverage inside high performance. Here's the challenge, as most users connect to WiMAX, while in the interior. In fact, according to Senza Fili Consulting, 75% of the estimated WiMAX operators that over 80% of its subscribers are connected to the WiMAX network, while in the interior.
More Most cases, indoor users have longer sessions and use more bandwidth intensive applications, resulting in the need for operators to ensure high capacity, and optimize indoor coverage. Therefore, for the best user experience in its class, improved indoor coverage is becoming a crucial task.
4.1 COVERAGE OF INTERNAL CHALLENGE IN WIMAX
The demand for indoor coverage comprehensive, high-density capacity translates into a need for a high density of BTS, with the number of BTS to grow as more users subscribe to services, using multiple devices and software applications. Further implement multisectoral macro STS is often not feasible or cost effective. For operators it becomes progressively more difficult and costly to accommodate a greater number of macro cells.
The equipment cost, although significant, is not often a major obstacle for dense deployments macro. site acquisition, site preparation and installation can have an even greater impact on capital spending in general. This may make it impossible for operators who operate in areas with high density of users to close their business case or return may be delayed unnecessarily.
As the number of BTS and traffic increases, operators must also carefully monitor the growth of costs of return. If traffic from each BTS has to be transported by a steel cable solution, OPEX costs can quickly escalate if each BTS has its own link. Depending on the location, the connection steel cable infrastructure (perhaps DSL or fiber) can be expensive and may not be easily accessible from some places (for example, lamp posts).
By contrast, wireless backhaul can significantly cap operating costs return, and then allows the operator to aggregate traffic so skip efficient and recurrent rates of return associated with each BTS deployed, but may require additional spectrum and additional equipment investment. On the other hand, stations repeater with integrated support for wireless backhaul eliminates the need for costly and lengthy process of preparing several sites for backhaul.
4.2 BEYOND THE MACRO BTS
In the early stages of most implementations of WiMAX network architecture focused on multi-sectoral, macro BTS prevails, and actually achieves a good outdoor coverage with a limited number of BTS. However, a network architecture around macro cells often do not scale well when the requirements for indoor coverage and high capacity becomes more urgent. The cost of hardware, acquisition and preparation site, and the installation quickly outstrips the income opportunity, making it difficult to achieve a positive ROI.
To address the requirements of the new coverage and capacity, operators need to implement more compact, smaller than the BTS backhaul support cost-effective solutions. They also come with less onerous requirements and site acquisition costs, and that can be installed in various places of access (lampposts, building walls), closer at street level, and use less energy. Due to their small size and weight, it is easier for operators to access the mobile stations and meet regulatory requirements.
The upcoming IEEE 802.16j bring greater support for the integration of wireless backhaul WiMAX. This demonstrates the commitment of industry to provide standards-based solution for more compact BTS to support the return of the wireless band.
Table 1: Options for WiMAX BTS
WiMAX operators have started exploring alternative network architectures that can be used to increase the initial macro infrastructure, and are also increasingly used by cellular operators for boost capacity and indoor coverage. These options are based on different types of BTS (Table 1) that form a network of base to be used to extend indoor coverage and increase the capacity available for domestic subscribers. They are:
- Micro or pico cell outdoor locations in the vicinity of the buildings they cover. Outdoor microcells and Pico cells are smaller and less expensive than macro BTS, multisectoral, but generally have a more limited range and if they have a single sector, the more limited. They are typically used in urban areas with high concentrations of users and traffic. Used in dense networks, where each cell covers a small area, ensuring good coverage and high capacity. They can be located on utility poles, roofs, or walls of the building. Microcell cells and Pico can use wire line or wireless backhaul. mesh topologies can be adopted, wireless backhaul is fully integrated the BTS.
- Pico cells in indoor public places or buildings of the company, to provide a high density capability and covers a building. interior solutions are often the only way to provide deep coverage in construction. They are smaller than microcells outdoor and Pico cells, and their cost and ease of installation is even smaller because it can be mounted on walls or ceilings. Picocells can use wireless backhaul or cable, depending on the reliability and cost of connectivity options available. Links cheap broadband cable, where available, often turn out to be most viable solutions. In buildings where cable connectivity is not available to the operator or are too expensive, wireless backhaul can be used instead.
- Extension of residential and small business coverage with femtocells. Self-installable, low-cost femtocells can be used to improve coverage in homes or small offices. Are based on the DSL or cable modem broadband connection available for return. The operator is usually not involved installation directory of femtocells. Subscribers tend to buy in a store and install in your home or office.
5. STRATEGIES TO ENHANCE THE INTERIOR OF WIMAX COVERAGE
In general, the wireless broadband industry focuses on the backend system (Radio Access network or core network) to optimize the network, especially on improving indoor coverage. As WiMAX is concerned, WiMAX modems are often treated as an access device connectivity to end users, whose function is merely to transmit and receive. It is time that the device receives more credit and trust with a larger role - Improved indoor coverage.
There are four methods that can be used for WiMAX modems to play a role in improving indoor coverage:
1) Improving the uplink reception (through next generation antenna technology)
2) Use proper type of antenna
3) The optimal positioning of the modem
4) Increase indoor WiFi coverage
Figure 4: WiMAX role in improving indoor coverage
5.1 Better UP ENTERTAINMENT
Not many technologies introduced by the base stations as 4T4R MIMO A radio unit on the top of the tower to reduce power loss and higher power transmission. Unfortunately, these technologies do little to improve reception of uplink is often the bottleneck that limits coverage indoors. uplink connection is usually weaker than downlink and uplink connection is enabled by an internal modem transmitter is low power (200mW) compared with a base station transmitter (10W). Therefore, the coverage link connection is always limited.
Figure 5 illustrates the downlink and uplink connection coverage using different antenna technologies. The link connection loss (A) occurs in a distance long before the loss of downlink connection (Points B, C and D) and at this point, internal modems can no longer connect to the base station. Although MIMO A and beam forming can extend the reception of downlink (points B, C and D), these technologies do not contribute in promoting the reception of link upward.
Figure 5: uplink and downlink to cover the antenna technologies different
There are several technologies that can improve uplink performance. One popular method is switched requiring Tx Diversity extra antenna and includes an algorithm to determine the transmission path based on the best antenna. This method allows the modem to transmit radio signals the best antenna to improve the overall strength of signal transmission, with the slight disadvantage of an additional switch and minimum power loss.
A better method available is a double emitter with cyclic delay diversity (CDD 2Tx), which requires two power amplifiers (PA) and two antennas. This method can improve further global transmission of the signal intensity. CDD 2Tx addition, an alternative method with the added performance is 2Tx Space Time Coding (STC). However R1.5 WiMAX base stations must be capable of supporting the STC for users to enjoy a better uplink performance.
Figure 6 explains how the uplink performance can be extended by switching Tx Diversity (E), double emitter with Cyclic Delay Diversity (Section F) 2Tx space and time encoding (G). It is important to note that only one of these technologies can be used at any time.
Figure 6: Uplink performance can be extended through next generation technologies antenna
5.2 PROPER USE OF TYPE ANTENNA
antenna design is often considered a black art. There are many factors that can affect the antenna performance. For example, factors such as material, length, type and design of the antenna contribute to the real antenna gain.
The common type of antennas used patch antennas and omnidirectional antennas. patch antenna consists of one or more conductive plates separated above and parallel to a plane ground. This design allows the patch antenna to the radiation patterns that are very directional. On the other hand, omnidirectional antennas are made from a piece of material conductor generally orthogonal to the plane of the floor. This design allows omni-directional antennas to radiate signals perpendicular to the antenna in a uniform manner.
Figure 7 illustrates the 3D radiation pattern for the patch and omni antennas. Red indicates the most sensible place or area with the greatest gain relative to the antenna. In the diagram, it is obvious that the patch antenna has a strong directionality, therefore, the modem must be positioned correctly to ensure that the modem surface emitting radiation patterns compared to the base station for optimal performance.
Figure 7: Review and radiation pattern of an omnidirectional antenna
However, signals omni antenna radiates uniformly in a plane and need not to deal with the base station in a predetermined direction. Therefore, it is ideal for indoor use, where the exact location of the nearest base station is difficult to determine.
OPTIMAL PLACEMENT 5.3 MODEM
It is important to note that signals WiMAX is broadcast via radio waves and indoor care placement can significantly increase the indoor coverage.
Operators WiMAX should educate users about where and how to place your internal modem. First, simply place the internal modem near the window overlooking the station nearest base, as shown in Figure 8 can improve antenna performance dramatically. This is due to the loss of penetration of radio waves glass (6 dB) is much less than the loss of penetration of concrete walls (13 dB or more.)
Figure 8: An indoor WiMAX modem compared to the base station
Second, place the modem near the front window at a distance window yields better performance as a result of improved indoor coverage. Observation and trial tests.
5.4 INTERNAL PROMOTION COVERAGE WITH WIFI
Some users can express that is not always appropriate to restrict the use of a computer area that is next to the window. In addition, you may want the convenience and flexibility of wireless network share broadband connection via WiFi.
Therefore, using Wi-Fi to complement WiMAX can provide benefits that improve indoor coverage. One of the ways to go about this is to use a combination of WiMAX-WiFi modem also known as WiMAX integrated access devices (IAD) that enables WiMAX-WiFi-In-Out. Wi-Fi transmitters and WiMAX are placed inside the modem itself so that the transmitters are able to connect to devices Wi-Fi-enabled WiMAX base stations and respective simultaneously.
For example, as illustrated in Figure 9 below, the user can place indoor WiMAX modem optimal place (usually near a window) and enjoy WiMAX through the flexibility of multiple devices with Wi-Fi within the perimeter of the home or small office.
Figure 9: Place the WiMAX for better indoor coverage
However, with both WiMAX and WiFi on the device itself has a price. In many countries, especially in Asia and the U.S., WiMAX offers in the frequency band 2.3 GHz and 2.5 GHz, which almost coincides with the frequency band is 2.4GHz WiFi. When the share of WiMAX and WiFi radio frequencies around, interference may occur and jeopardize connectivity. To overcome the problem of interference, modem carefully designed is necessary to enable both wireless technologies to coexist on the same device.
The advantage of combining Modem is WiFi-WiMAX antennas can be optimally designed to isolate radio interference in a very controlled. Moreover, since the antennas are fixed the modem, there is better control over the Wi-Fi and WiMAX radio signals to ensure that users get the best WiFi and WiMAX connectivity in the same place.
6. LTE MODEL FOR COVERAGE OF INTERIOR
The challenges presented by 3G/Universal Mobile Telecommunications System (UMTS) to stringent requirements of LTE. The Third Generation Partnership Project (3GPP) has developed specifications for LTE as an evolution of UMTS. It is created to provide a number benefits including increased capacity and lower latency, spectral efficiency and cell edge performance, and to provide GSM / HSPA and CDMA / EVDO service providers a migration path to a 4G platform that deals with interoperability issues.
However, the benefits of LTE evolution only will be felt if the service providers to effectively reach their customers. In 2009, ABI Research report, it is expected that by 2013 over 67% of all teams delivered will be able to 3G +. The volume of mobile traffic from inside buildings, is already more than 60% for voice calls and is expected to grow by above 90% for data sessions. Taking the technical issues and user patterns together, we can see that most of the opportunity of income data Mobile telephony is in the buildings. It is therefore essential to be everywhere in the building wireless coverage and is an issue to be addressed both service provider and the subscriber alike.
Poor indoor wireless coverage is now recognized worldwide as one of the biggest obstacles facing today's mobile subscribers. This is particularly acute and data services licenses LTE published in frequencies of up to 2.6 GHz with a promise to discharge 100 Mbps and 50 Mbps upload speeds per cell. There are many issues to be considered for effective coverage in wireless building with some of the key questions asked by those seeking to implement a solution for LTE.
6.1 DIFFERENT SOLUTIONS
Traditionally, mobile networks are designed with an 'out' approach, where the service provider uses the macro and micro networks to penetrate in buildings. With most of the sessions originating from the building with modern construction techniques, environmentally friendly and energy efficient and materials, the penetration of the buildings of the macro network is no longer viable. Therefore service providers, building owners and businesses should implement systems to provide wireless coverage in force from the building. This is the only way to maintain a good sign and meet service levels and data rates required by current subscribers of mobile broadband, while ensuring efficient use of network infrastructure services provider.
LTE comes with the choice of antenna diversity provided by multiple-in-multiple-output (MIMO). MIMO was developed for outdoor deployments and there is a great debate about the need for MIMO implementations in a building. There is also uncertainty about whether it is profitable. However, there may be specific projects in which MIMO can be a benefit, so it is important that any solution deployed must have this coverage flexibility available. budgets of careful planning antenna sites and link coverage solution to ensure compliance edge of the cell phone user needs to provide adequate bandwidth.
6.2 FREQUENCY AND duplexer
The standard allows both LTE Frequency Division Duplex (FDD) and Time Division Duplex (TDD) variants with licenses that are seen across a wide range of frequencies including 700MHz, 800MHz, 900MHz, 1800MHz, 2100MHz and 2600MHz. The ITB 2009 on wireless in construction has found that LTE deployments in China is almost certain to TDD. This presents a challenge when selecting an appropriate technology in building coverage wireless has the flexibility to support all these options and variants. In implementations for multiple operators, it is possible for multiple frequencies systems and thus duplex required in the same system. In addition, as a display of multiple operators may also need support existing 2G and 3G services at the same time.
There are three main options available to improve coverage inside buildings including wireless repeaters distributed distributed radio and antenna solutions for Distributed Systems (DAS). DAS is generally favored a moderate to large infrastructure to provide better coverage and unified indoor wireless multiple services to lower capital costs and operating costs.
6.3 DISTRIBUTION ANTENNA SYSTEM
distributed antenna system (DAS) comprises a network of antennas that are placed throughout a building dedicated to providing coverage inside buildings. Traditionally, two types of available DAS, liabilities and assets. Hybrid solutions are also used in the active units are distributed in building a network with each meal small passive antenna.
Passive DAS is a network of coaxial cables, couplers and power dividers to distribute wireless signals through buildings. ABI Research identifies in its 2009 report that passive DAS systems are known for suffering major losses in higher frequencies
and therefore not easily conducive to LTE. It also recognizes that buildings over 20,000 m2 is needed active deployment of the DAS.
Active DAS service feeds from a base station or repeater amplifies the wireless signal distribution within buildings through fiber optic cable RF, which connect to multiple remote antenna units positioned in different areas of the building. In the past there has been a question with DAS solutions assets relating to its ability to TDD support and frequencies simultaneously in a single hardware infrastructure. With the additional hardware appears in order to add in services at a later date, not conceal the financial implications for the improvement of many active DAS solutions.
More recently, another cost effective option is DAS introduced which has had a real broadband, proactive approach. This alternative DAS while compatible with any number or combination of wireless, protocols, duplexing systems or frequencies in a system without the need for specific services overlap. The system has the ability to support any type of service, it also provides peace of mind to future proof new investments in building wireless infrastructure, enabling new services being added, without additional components or costly upgrades.
7. SUMMARY
Increasingly, WiMAX operators have started to seek solutions that meet their strict coverage and capacity needs with scalable network architecture, flexible and cost effective. The strategy operators choose to enhance coverage and capacity will have a material impact on its network plans from the beginning. As the initial network plan can facilitate or impede future infrastructure expansion, which is crucial to begin to address the issues of indoor coverage and high capacity density during the early planning stages network.
There is no single solution. Operators should have a look at your market, and understand what the market needs and challenges physical environment are. Most likely, each operator is a different solution for the best coverage and capacity needed in a cost effective way. There is no way yet established and a limited selection of products. However, the high capacity and improved coverage are issues whose importance is rapidly increasing as demand for services grows and WiMAX mobile devices make their appearance on the market.
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About the Author
K.RAVI
Assist.Professor
Dept. of Informatics
Alluri Institute of Management Sciences
Hunter Road, Warangal, A.P., India.
e-Mail ID: kolipakaravi@yahoo.co.in
Building A Turnout, Step 12 - Cutting The Gaps In The Rail
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