WiMAX Modems in the Network and Indoor Coverage

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WiMAX Modems in the Network and Indoor Coverage

K.Ravi

Assist. Professor

Dept. of Informatics

kolipakaravi@yahoo.co.in

ABSTRACT:

WiMAX has enabled convergence of mobile and fixed broadband networks through a common wide-area radio-access technology and flexible network architecture. Since January 2007, the IEEE 802.16 Working Group has been developing a new amendment of the IEEE 802.16 standard (i.e., IEEE 802.16m) as an advanced air interface to meet the requirements of ITU-R/IMT-advanced for 4G systems, as well as for the next-generation mobile network operators.

With WiMAX indoor traffic taking up more than 80% of total WiMAX traffic, WiMAX Operators are faced with the pressing need to improve indoor coverage. Contrary to common belie f that WiMAX Modems are merely variables in the WiMAX subsystem, this whitepaper discusses how WiMAX Modems can play a major role in the subsystem, particularly in improving indoor coverage.

Keywords- WiMAX, Modems, Networks, Indoor Coverage, Antenna

INTRODUCTION:

The growth of WiMAX has been tremendous. Maravedis predicts that there will be an accumulated 55 million WiMAX subscribers by the end of 2012. While the growth deserves to be applauded, there is a significant concern in terms of providing quality indoor coverage to meet user expectations. Indoor coverage has always been a known challenge for wireless technologies and it does not differ with WiMAX, though high spectrum utilization and throughput are the prominent advantages of this technology.

As such, WiMAX Operators around the world have an urgent need to optimize indoor coverage as most often users access the network from indoor locations. According to Senza Fili Consulting, 75% of WiMAX Operators estimate that over 80% of their subscribers will connect to the WiMAX network from indoors. A contributing factor towards poor indoor coverage is WiMAX high operating frequency range, which makes it difficult for radio waves to penetrate through buildings. Currently, numerous initiatives focus on the backend system (Radio Access Network or Core Network) to optimize the network, however, at the end of the day, indoor coverage remains unsatisfactory.

This whitepaper encourages the WiMAX industry to view this issue from a different perspective. We see that WiMAX Modems can play an active role as part of the subsystem to improve indoor coverage, contrary from current perception that modems merely extend connectivity to end users. There are 4 methods that can be employed by WiMAX Modems to enhance indoor coverage

• Improving uplink reception through antenna technology

• Use of appropriate antenna type

• Optimal modem placement

• Boosting indoor coverage with WiFi

Indoor Coverage:

WiMAX is fast gaining momentum and is widely adopted by many residential and business subscribers worldwide. In fact, according to WiMAX Forum®, 2009 concluded with approximately 523 deployments globally, a 28% increase compared to 2008. WiMAX in general promises ubiquitous connectivity, access for both fixed and mobile devices and supports bandwidth-hungry applications without sweat. However, similar to other wireless broadband technologies in the market, the underlying issue for WiMAX remains in providing high performance indoor coverage. Here lies the challenge, as most users would connect to WiMAX while indoors. In fact, according to Senza Fili Consulting, 75% of WiMAX Operators estimate that over 80% of their subscribers will connect to the WiMAX network while indoors.

More often than not, indoor users have longer sessions and use more bandwidth intensive applications, resulting in the need for Operators to ensure high capacity in addition to optimized indoor coverage. Therefore, for best-in-class user experience, improving indoor coverage is becoming a very crucial task.

Frequency vs. Coverage:

Most WiMAX Operators operate in the 2.3GHz, 2.5GHz, or 3.5GHz frequency range. At these high frequencies, radio waves tend to have high transmission loss, poor ability for diffraction, and most importantly, poor building penetration capability. According to Andrea Goldsmith in her book Wireless Communications, there is a 6dB penetration loss for glass window and 13dB loss for concrete walls. With this in mind, indoor performance is further reduced when signals are required to penetrate walls. Figure 1 illustrates this by comparing the signal strength performance between a wall and window. As a result of having lower penetration loss, signals that penetrate the window emerge stronger (proved by the higher signal strength as shown in Figure 1) and translates into improved indoor performance.

Additionally, due to the high frequency bands of WiMAX which weakens indoor penetration capabilities, the coverage distance achieved is lower. Figure 2 compares the indoor and outdoor coverage distances for dense urban, urban and rural areas across the 2.5GHz and 3.5GHz frequency bands. It is evident that 3.5GHz (the highest WiMAX frequency) produces shorter coverage distance.

Indoor Coverage Improvement Strategies for WiMAX:

In short, lowering the frequency is probably the answer to improve indoor coverage. While the WiMAX industry is looking forward to accelerated developments on the lower frequency band, 700 MHz, experts believe it might take a couple of years to reach full fruition considering the vast technical specifications involved.

What then is a more immediate and effective solution to improve indoor coverage?

Smart CPE Antenna Systems:

A smart antenna system is one that has circuit elements associated with its radiating elements such that the antenna properties are controlled by the received signal A smart CPE antenna can be made up of a combination of from 2 to as many antenna elements as are needed to maximize the required antenna performance.

There is however a trade off, a greater the number of antenna elements [more sectors] results in:

1. Narrower the instantaneous azimuth beamwidth

2. Higher gain [C/N]

3. Larger the physical dimensions

4. Better selectivity

5. less interference [C/I]

Practically Smart CPE Antenna arrays are made up of from 4 to 8 antenna elements An additional consideration is that given the same Azimuth beamwidth and the same number of elements an increase in the length of the antenna elements will deliver increased gain.

MTI Smart WIMAX CPE:

The MTI smart WIMAX indoor CPE is a compact and easy to integrate, switch selectable antenna array specifically designed to meet the needs of the WIMAX market. The antenna which includes the solid state RF switch is designed to be either integrated as part of the radio, or, supplied as a separate unit to be added on to the radio by the end user.

The antenna provides full 360 deg coverage by multi directional high gain beams. The high gain directional beams provide better RF link budgets with the base station and reduce side lobes interference. The smart CPE antenna can include 4 to 8 elements with the integral solid state RF switch controlling the active sector. The higher the number of beams the higher the gain provided by each beam and the narrower the beam width.

MTI Smart CPE antenna arrays are currently offered in variety of frequencies bands and azimuth beam widths delivering element gain between 6 and 9.5 dBi per sector dependant on the frequencies beam width:

Frequencies bands:

3.3-3.5, 3.4-3.6, 3.5-3.8, 4.9-5.03, 5.15-5.35, 5.47-5.825 GHz

Beam widths delivering 360° coverage:

4 elements spanning 90° per element

6 elements of 60° per element

8 elements of 45° per element.

Smart Array Cost Tradeoff:

The number of beams, gain, and beam width is a tradeoff of the price. The higher the number of antennas elements making up the array the higher the gain – the larger the size and higher the price. Lower gain results in reduced size and price.

3×120º, 4×90º and 6×60º Arrays:

One of 4 elements spanning 90° per segment,

One of 6 elements spanning 60° per segment,

One of 8 elements spanning 45° per segment.

WiMAX Modems as part of the Subsystem:

Generally, the wireless broadband industry focuses on the backend system (Radio Access Network or Core Network) to optimize network, particularly in improving indoor coverage. As far as WiMAX is concerned, WiMAX Modems are often treated as a connectivity access device for end users, whose role is merely to transmit and receive. It is time the device receives more credit and is trusted with a more important role – improving indoor coverage.

There are 4 methods which can be employed by WiMAX Modems to play a part in improving indoor coverage:

• Improving uplink reception (through next generation antenna technologies)

• Use of appropriate antenna type

• Optimal modem placement

• Boosting indoor coverage with WiFi

Improving Uplink Reception (Through Next Generation Antenna Technologies):

There are many technologies introduced by base stations such as 4T4R MIMO A, radio unit on top of tower to reduce feeder loss and higher transmission power. Unfortunately, these technologies do very little to boost uplink reception which is often the bottleneck that limits indoor coverage. Uplink connection is usually weaker than downlink, as uplink connection is enabled by an indoor modem transmitter which has lower power (200mW) compared to that of a base station transmitter (10W). Hence, the coverage of uplink connection is always limited.

There are several technologies that can improve uplink performance. One of the popular methods is Switched Tx Diversity which requires an extra antenna and includes an algorithm to determine transmission based on the path of the better antenna. This method allows the modem to transmit radio signals from the best antenna to improve overall transmission signal strength, with the slight tradeoff of an extra switch and minimal loss of power. An improved method available is Dual Transmitter using Cyclic Delay Diversity (2Tx CDD) which requires two power amplifiers (PA) and two antennas. This method can further improve the overall transmission signal strength. Aside from 2Tx CDD, an alternate method with added performance is 2Tx Spatial Time Coding (STC). However WiMAX R1.5 base stations must be able to support STC for users to enjoy better uplink performance.

Use of Appropriate Antenna Type:

Antenna design is often regarded as a black art. There are many factors that can affect antenna performance. For example, factors such as material, length, type and antenna design contribute to the actual antenna gain. The common type of antennas used is patch antennas and omni antennas. Patch antennas are made up of one or several conductive plates that are spaced above and parallel to a ground plane. This design enables patch antennas to have radiation patterns that are very directional. On the other hand, omni antennas are made from a piece of conductive material generally orthogonal to the ground plane. This design enables omni antennas to radiate signals perpendicular to the antenna uniformly.

Optimal Modem Placement:

It is important to note that WiMAX signals are emitted through radio waves and careful indoor placement can significantly boost indoor coverage. As such, WiMAX Operators should educate users on where and how to place their indoor modem. Firstly, by simply placing the indoor modem near the window that faces the nearest base station as shown in Figure 7 can improve the antenna performance  dramatically. This is because radio wave penetration loss for glass (6dB) is much lower than the penetration loss for concrete walls (13dB or more).

Secondly, placing the modem near the window as opposed to a distance away from the window yields better throughput as a result of improved indoor coverage. From observation and trial runs conducted, Greenpacket estimates a throughput reduction of 20-40% when the modem is placed 10m away from the window (and deeper into the room). However, this finding is subjective and may vary in different countries, depending on distance from base station and RF environments.

Boosting Indoor Coverage with WiFi:

Some users might express that is it not always convenient to restrict computer usage to an area that is next to the window. Additionally, they might want the convenience and flexibility of sharing the wireless broadband connection through WiFi. Therefore, using WiFi to complement WiMAX can provide advantages that improve indoor coverage. One of the ways of going about this is to use a WiMAX-WiFi combination modem also known as WiMAX Integrated Access Device (IAD) which enables WiMAX-In-WiFi-Out. WiFi and WiMAX transmitters are placed within the same modem so that the transmitters are able to connect to the respective WiFi-enabled devices and WiMAX base stations simultaneously.

However, having both WiMAX and WiFi in the same device comes with a price. In many countries, especially in Asia and US, WiMAX is offered on the 2.3GHz and 2.5GHz frequency band which almost coincides with the frequency band of WiFi which is 2.4GHz. When WiMAX and WiFi share approximate radio frequencies, interference can occur and jeopardize connectivity. To overcome the issue of interference, a carefully designed modem is required to allow both wireless technologies to co-exist in the same device. The advantage of having the WiFi-WiMAX combination modem is that antennas can be optimally designed to isolate radio interferences in a highly controlled manner. In addition, since antennas are stationary within the modem, there is better control over the WiFi and WiMAX radio signals to ensure users gain the best WiFi and WiMAX connectivity in the same location.

Improved Indoor Coverage:

Improving current WiMAX indoor coverage is an urgent need for most operators. At Greenpacket, through extensive R&D efforts, we have produced WiMAX Modems that go beyond merely enabling connectivity. Our modems are designed to work harder for WiMAX Operators, particularly in the area of improving indoor coverage. Briefly, Greenpacket’s next generation indoor modems boast of the following key features which make them ideal in boosting indoor coverage:

1. Ideal to be placed near a window The exterior design is able to withstand high temperatures and can be placed near the window for better coverage. Selected USB models have suction cups which can be fixed to a window for optimum indoor coverage.

2. Boost indoor coverage with WiFi Built-in WiFi capabilities for convenient wireless access around the home/SOHO.

3. High gain Omni antenna Greenpacket’s indoor modems are built with Omni antenna that radiate and receive WiMAX signals from any direction for great flexibility in modem placement and all-direction performance. The high gain antenna ensures WiMAX signals are transmitted in spite of penetration loss, resulting in improved indoor signal indoors.

4. Improved uplink coverage Our modems deploy Switched Tx Diversity, a next generation antenna technology which intelligently selects the best antenna during transmission to increase signal strength for improved uplink performance.

WiMAX Modems in the Network and Indoor Coverage

K.Ravi

Assist. Professor

Dept. of Informatics

kolipakaravi@yahoo.co.in

ABSTRACT:

WiMAX has enabled convergence of mobile and fixed broadband networks through a common wide-area radio-access technology and flexible network architecture. Since January 2007, the IEEE 802.16 Working Group has been developing a new amendment of the IEEE 802.16 standard (i.e., IEEE 802.16m) as an advanced air interface to meet the requirements of ITU-R/IMT-advanced for 4G systems, as well as for the next-generation mobile network operators.

With WiMAX indoor traffic taking up more than 80% of total WiMAX traffic, WiMAX Operators are faced with the pressing need to improve indoor coverage. Contrary to common belie f that WiMAX Modems are merely variables in the WiMAX subsystem, this whitepaper discusses how WiMAX Modems can play a major role in the subsystem, particularly in improving indoor coverage.

Keywords- WiMAX, Modems, Networks, Indoor Coverage, Antenna

INTRODUCTION:

The growth of WiMAX has been tremendous. Maravedis predicts that there will be an accumulated 55 million WiMAX subscribers by the end of 2012. While the growth deserves to be applauded, there is a significant concern in terms of providing quality indoor coverage to meet user expectations. Indoor coverage has always been a known challenge for wireless technologies and it does not differ with WiMAX, though high spectrum utilization and throughput are the prominent advantages of this technology.

As such, WiMAX Operators around the world have an urgent need to optimize indoor coverage as most often users access the network from indoor locations. According to Senza Fili Consulting, 75% of WiMAX Operators estimate that over 80% of their subscribers will connect to the WiMAX network from indoors. A contributing factor towards poor indoor coverage is WiMAX high operating frequency range, which makes it difficult for radio waves to penetrate through buildings. Currently, numerous initiatives focus on the backend system (Radio Access Network or Core Network) to optimize the network, however, at the end of the day, indoor coverage remains unsatisfactory.

This whitepaper encourages the WiMAX industry to view this issue from a different perspective. We see that WiMAX Modems can play an active role as part of the subsystem to improve indoor coverage, contrary from current perception that modems merely extend connectivity to end users. There are 4 methods that can be employed by WiMAX Modems to enhance indoor coverage

• Improving uplink reception through antenna technology

• Use of appropriate antenna type

• Optimal modem placement

• Boosting indoor coverage with WiFi

Indoor Coverage:

WiMAX is fast gaining momentum and is widely adopted by many residential and business subscribers worldwide. In fact, according to WiMAX Forum®, 2009 concluded with approximately 523 deployments globally, a 28% increase compared to 2008. WiMAX in general promises ubiquitous connectivity, access for both fixed and mobile devices and supports bandwidth-hungry applications without sweat. However, similar to other wireless broadband technologies in the market, the underlying issue for WiMAX remains in providing high performance indoor coverage. Here lies the challenge, as most users would connect to WiMAX while indoors. In fact, according to Senza Fili Consulting, 75% of WiMAX Operators estimate that over 80% of their subscribers will connect to the WiMAX network while indoors.

More often than not, indoor users have longer sessions and use more bandwidth intensive applications, resulting in the need for Operators to ensure high capacity in addition to optimized indoor coverage. Therefore, for best-in-class user experience, improving indoor coverage is becoming a very crucial task.

Frequency vs. Coverage:

Most WiMAX Operators operate in the 2.3GHz, 2.5GHz, or 3.5GHz frequency range. At these high frequencies, radio waves tend to have high transmission loss, poor ability for diffraction, and most importantly, poor building penetration capability. According to Andrea Goldsmith in her book Wireless Communications, there is a 6dB penetration loss for glass window and 13dB loss for concrete walls. With this in mind, indoor performance is further reduced when signals are required to penetrate walls. Figure 1 illustrates this by comparing the signal strength performance between a wall and window. As a result of having lower penetration loss, signals that penetrate the window emerge stronger (proved by the higher signal strength as shown in Figure 1) and translates into improved indoor performance.

Additionally, due to the high frequency bands of WiMAX which weakens indoor penetration capabilities, the coverage distance achieved is lower. Figure 2 compares the indoor and outdoor coverage distances for dense urban, urban and rural areas across the 2.5GHz and 3.5GHz frequency bands. It is evident that 3.5GHz (the highest WiMAX frequency) produces shorter coverage distance.

Indoor Coverage Improvement Strategies for WiMAX:

In short, lowering the frequency is probably the answer to improve indoor coverage. While the WiMAX industry is looking forward to accelerated developments on the lower frequency band, 700 MHz, experts believe it might take a couple of years to reach full fruition considering the vast technical specifications involved.

What then is a more immediate and effective solution to improve indoor coverage?

Smart CPE Antenna Systems:

A smart antenna system is one that has circuit elements associated with its radiating elements such that the antenna properties are controlled by the received signal A smart CPE antenna can be made up of a combination of from 2 to as many antenna elements as are needed to maximize the required antenna performance.

There is however a trade off, a greater the number of antenna elements [more sectors] results in:

1. Narrower the instantaneous azimuth beamwidth

2. Higher gain [C/N]

3. Larger the physical dimensions

4. Better selectivity

5. less interference [C/I]

Practically Smart CPE Antenna arrays are made up of from 4 to 8 antenna elements An additional consideration is that given the same Azimuth beamwidth and the same number of elements an increase in the length of the antenna elements will deliver increased gain.

MTI Smart WIMAX CPE:

The MTI smart WIMAX indoor CPE is a compact and easy to integrate, switch selectable antenna array specifically designed to meet the needs of the WIMAX market. The antenna which includes the solid state RF switch is designed to be either integrated as part of the radio, or, supplied as a separate unit to be added on to the radio by the end user.

The antenna provides full 360 deg coverage by multi directional high gain beams. The high gain directional beams provide better RF link budgets with the base station and reduce side lobes interference. The smart CPE antenna can include 4 to 8 elements with the integral solid state RF switch controlling the active sector. The higher the number of beams the higher the gain provided by each beam and the narrower the beam width.

MTI Smart CPE antenna arrays are currently offered in variety of frequencies bands and azimuth beam widths delivering element gain between 6 and 9.5 dBi per sector dependant on the frequencies beam width:

Frequencies bands:

3.3-3.5, 3.4-3.6, 3.5-3.8, 4.9-5.03, 5.15-5.35, 5.47-5.825 GHz

Beam widths delivering 360° coverage:

4 elements spanning 90° per element

6 elements of 60° per element

8 elements of 45° per element.

Smart Array Cost Tradeoff:

The number of beams, gain, and beam width is a tradeoff of the price. The higher the number of antennas elements making up the array the higher the gain – the larger the size and higher the price. Lower gain results in reduced size and price.

3×120º, 4×90º and 6×60º Arrays:

One of 4 elements spanning 90° per segment,

One of 6 elements spanning 60° per segment,

One of 8 elements spanning 45° per segment.

WiMAX Modems as part of the Subsystem:

Generally, the wireless broadband industry focuses on the backend system (Radio Access Network or Core Network) to optimize network, particularly in improving indoor coverage. As far as WiMAX is concerned, WiMAX Modems are often treated as a connectivity access device for end users, whose role is merely to transmit and receive. It is time the device receives more credit and is trusted with a more important role – improving indoor coverage.

There are 4 methods which can be employed by WiMAX Modems to play a part in improving indoor coverage:

• Improving uplink reception (through next generation antenna technologies)

• Use of appropriate antenna type

• Optimal modem placement

• Boosting indoor coverage with WiFi

Improving Uplink Reception (Through Next Generation Antenna Technologies):

There are many technologies introduced by base stations such as 4T4R MIMO A, radio unit on top of tower to reduce feeder loss and higher transmission power. Unfortunately, these technologies do very little to boost uplink reception which is often the bottleneck that limits indoor coverage. Uplink connection is usually weaker than downlink, as uplink connection is enabled by an indoor modem transmitter which has lower power (200mW) compared to that of a base station transmitter (10W). Hence, the coverage of uplink connection is always limited.

There are several technologies that can improve uplink performance. One of the popular methods is Switched Tx Diversity which requires an extra antenna and includes an algorithm to determine transmission based on the path of the better antenna. This method allows the modem to transmit radio signals from the best antenna to improve overall transmission signal strength, with the slight tradeoff of an extra switch and minimal loss of power. An improved method available is Dual Transmitter using Cyclic Delay Diversity (2Tx CDD) which requires two power amplifiers (PA) and two antennas. This method can further improve the overall transmission signal strength. Aside from 2Tx CDD, an alternate method with added performance is 2Tx Spatial Time Coding (STC). However WiMAX R1.5 base stations must be able to support STC for users to enjoy better uplink performance.

Use of Appropriate Antenna Type:

Antenna design is often regarded as a black art. There are many factors that can affect antenna performance. For example, factors such as material, length, type and antenna design contribute to the actual antenna gain. The common type of antennas used is patch antennas and omni antennas. Patch antennas are made up of one or several conductive plates that are spaced above and parallel to a ground plane. This design enables patch antennas to have radiation patterns that are very directional. On the other hand, omni antennas are made from a piece of conductive material generally orthogonal to the ground plane. This design enables omni antennas to radiate signals perpendicular to the antenna uniformly.

Optimal Modem Placement:

It is important to note that WiMAX signals are emitted through radio waves and careful indoor placement can significantly boost indoor coverage. As such, WiMAX Operators should educate users on where and how to place their indoor modem. Firstly, by simply placing the indoor modem near the window that faces the nearest base station as shown in Figure 7 can improve the antenna performance  dramatically. This is because radio wave penetration loss for glass (6dB) is much lower than the penetration loss for concrete walls (13dB or more).

Secondly, placing the modem near the window as opposed to a distance away from the window yields better throughput as a result of improved indoor coverage. From observation and trial runs conducted, Greenpacket estimates a throughput reduction of 20-40% when the modem is placed 10m away from the window (and deeper into the room). However, this finding is subjective and may vary in different countries, depending on distance from base station and RF environments.

Boosting Indoor Coverage with WiFi:

Some users might express that is it not always convenient to restrict computer usage to an area that is next to the window. Additionally, they might want the convenience and flexibility of sharing the wireless broadband connection through WiFi. Therefore, using WiFi to complement WiMAX can provide advantages that improve indoor coverage. One of the ways of going about this is to use a WiMAX-WiFi combination modem also known as WiMAX Integrated Access Device (IAD) which enables WiMAX-In-WiFi-Out. WiFi and WiMAX transmitters are placed within the same modem so that the transmitters are able to connect to the respective WiFi-enabled devices and WiMAX base stations simultaneously.

However, having both WiMAX and WiFi in the same device comes with a price. In many countries, especially in Asia and US, WiMAX is offered on the 2.3GHz and 2.5GHz frequency band which almost coincides with the frequency band of WiFi which is 2.4GHz. When WiMAX and WiFi share approximate radio frequencies, interference can occur and jeopardize connectivity. To overcome the issue of interference, a carefully designed modem is required to allow both wireless technologies to co-exist in the same device. The advantage of having the WiFi-WiMAX combination modem is that antennas can be optimally designed to isolate radio interferences in a highly controlled manner. In addition, since antennas are stationary within the modem, there is better control over the WiFi and WiMAX radio signals to ensure users gain the best WiFi and WiMAX connectivity in the same location.

Improved Indoor Coverage:

Improving current WiMAX indoor coverage is an urgent need for most operators. At Greenpacket, through extensive R&D efforts, we have produced WiMAX Modems that go beyond merely enabling connectivity. Our modems are designed to work harder for WiMAX Operators, particularly in the area of improving indoor coverage. Briefly, Greenpacket’s next generation indoor modems boast of the following key features which make them ideal in boosting indoor coverage:

1. Ideal to be placed near a window The exterior design is able to withstand high temperatures and can be placed near the window for better coverage. Selected USB models have suction cups which can be fixed to a window for optimum indoor coverage.

2. Boost indoor coverage with WiFi Built-in WiFi capabilities for convenient wireless access around the home/SOHO.

3. High gain Omni antenna Greenpacket’s indoor modems are built with Omni antenna that radiate and receive WiMAX signals from any direction for great flexibility in modem placement and all-direction performance. The high gain antenna ensures WiMAX signals are transmitted in spite of penetration loss, resulting in improved indoor signal indoors.

4. Improved uplink coverage Our modems deploy Switched Tx Diversity, a next generation antenna technology which intelligently selects the best antenna during transmission to increase signal strength for improved uplink performance.

References:

1. Antenna Patterns and Their Meaning by Cisco Systems

2. DS230 Service Manual by Green Packet

3. DV230 Service Manual by Green Packet

4. A Practical Guide to WiMAX Antennas: MIMO and Beamforming Technical Overview by Motorola Corporation

5. Indoor, High-Capacity Coverage with WiMAX: How Are Operators Meeting The Challenge? By Senza Fili Consulting

6. Sequans Communications: from WiMAX to 4G by Sequans Communications

7. Wireless Communications by Andrea Goldsmith, Cambridge University Press

References:

1. Antenna Patterns and Their Meaning by Cisco Systems

2. DS230 Service Manual by Green Packet

3. DV230 Service Manual by Green Packet

4. A Practical Guide to WiMAX Antennas: MIMO and Beamforming Technical Overview by Motorola Corporation

5. Indoor, High-Capacity Coverage with WiMAX: How Are Operators Meeting The Challenge? By Senza Fili Consulting

6. Sequans Communications: from WiMAX to 4G by Sequans Communications

7. Wireless Communications by Andrea Goldsmith, Cambridge University Press

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