Comparing Mobile WiMAX to 1*EVDO and HSPA in 3G..

Evolution Data-Optimized (1*EVDO) and High-Speed Downlink Packet Access (HSDPA/HSPA) have evolved from 3G CDMA standards to provide data services over a network originally conceived for mobile voice services. These 3G enhancements have evolved from the 3G experiences and as a result, inherit both the advantages and limitations of legacy 3G systems. WiMAX on the other hand was initially developed for fixed broadband wireless access and is optimized for broadband data services. Since Mobile WiMAX has evolved from systme concepts initially designed for fixed wireless access, WiMAX faces the challenge of meeting the additional requirements necessary to support mobility. A point by point comparison of the attributes of Mobile WiMAX with 3G-based 1*EVDO and HSDPA/HSPA systems is useful in addressing how these technologies can meet future network requirements for mobile broadband data services.

• Common features

Several features, designed to enhance data throughput, are common to EVDO, HSDPA/HSPA and Mobile WiMAX including:

- Adaptive modulation and coding (AMC)

- Hybrid ARQ (HARQ)

- Fast schedulig

- Bandwidth efficient handoff

• Key advantages of Mobile WiMAX

Unlike the CDMA-based 3G systems, which have evolved from voice-centric systems, WiMAX was designed to meet the requirements necessary for the delivery of broadband data services as well as voice. The Mobile WiMAX physical layer is based on Scalable OFDMA technology. The new technologies employed for Mobile WiMAX result in lower equipment complexity and simpler management due to the all-IP core network and provide Mobile WiMAX systems with many other CDMA-based 3G systems including:

- Tolerance to Multipath and Self-Interference

- Scalable Channel Bandwidth

- Orthogonal Uplink Multiple Access

- Support for Spectrally-Efficient TDD

- Frequency-Selective Scheduling

- Fractional Frequency Reuse

-Fine Quality of Service (QoS)

- Advanced Antenna Technology

All the systems have adopted advanced technologies to improve data throughput. However Mobile WiMAX, is based on OFDM/OFDMA technology which is more suitable for broadband wireless data communication. In fact OFDM/OFDMA is one proposal being considered in 3GPP/3GPP2 as the solution for LTE and is generally accepted as being the basis for 4G. An OFDM/OFDMA-based systme has high granular resourece allocation, better uplink efficiency, and can support a full range of advanced antenna technologies. These capabilities offer the potential for significant spectral efficiency advantages and better QoS in both the downlink and uplink direction. Mobile WiMAX can slso dynamically adjust downlink/uplink ratio with TDD support providing greater flexibility and spectral efficiency advantages in supporting varied types of broadband traffic. In contrast, EVDO and HSPA, based on FDD, have a fixed asymmetric downlink/uplink ratio determined by the difference in downlink/uplink spectral efficiency and fixed FDD channel bandwidth. Additionally, Mobile WiMAX provides superior QoS and offers operators greater flexibility in implementing Service Level Agreements to meet varied customer requirements.

From a performance perspective, only Mobile WiMAX can transport DSL and cable-like services cost-effectively in a mobile environment. This is an essential requirement for the success of Mobile WiMAX, a technology aimed at delivering broadband mobile services ranging from real-time interactive gaming, VoIP, and streaming media to non-real-time web browsing and simple file transfers.

Other benefits of WiMAX include its open standard approach and healthy ecosystem. Hundreds of companies have contributed to the development of the technology and many companies have announced product plans for this technology. The broad industry participation with worldwide adoption of th estandard will ensure economies of scale that will help drive low cost of subscription and enable the deployment of broadband mobile services in both developed and emerging markets. With a scalable architecturem high data throughput and low cost of deployment Mobile WiMAX is a leading solution for wireless broadband services. By creating a common platform that addresses a wide range of market segments, Mobile WiMAX is well-positioned to experience a high global take rate.

Co-Existence of Mobile WiMAX and GSM in China..

Mobile WiMAX has been developed for high-speed data rate applicaitons especially in mobile environments compared with other IEEE 802 series standards. Because of scarce frequency resources, it is unavoidable to interfere the neighboring commercial mobile networks when mobile WiMAX system is deployed.

Wireless broadband targets to bring high-speed data to multitudes of people in various geographical locations where wired transmission is costly, inconvenient, or unavailable. WiMAX is one kind of technologies devoted to make broadband wireless commercially available to the market. Compared with fixed version WiMAX, mobile WiMAX, based on IEEE 802.16e amendment, is intended primarily for both stationary and mobile deployments and designed specifically to optimize performance of wireless links in the outdoor environment over the next couple of year.

Mobile WiMAX defines interoperable system profiles of base stations and terminals, which are targeted for licensed and licensed-exempt frequency bands around the world. WiMAX channel bandwidths are 1.25MHz, 5MHz, 10MHz and 20MHz, etc. Data bursts can be transmitted through either FDD or TDD mode. Furthermore, TDD mode is more attractive than FDD mode in WiMAX system because TDD mode WiMAX system will not require a pair of frequency bands. On the other hand, the frequency resources are very limited around the world and it is hard to find frequency band pairs to deploy FDD mode WiMAX system.

In China, more than 150MHz frequency bands, located in 400MHz, 1.8GHz and 2.3GHz, have been allocated to TDD mode wireless access technologies. Among these frequency bands, nearly 140MHz frequency bands are reserved to 3G TDD systems. And in the left frequency bands, only 1.8GHz frequency band is adjacent to the commercial mobile networks, DCS1800 DL, which were deployed by China Mobile and China Unicom (DCS1800 is based on GSM technology which is deployed in 1800MHz frequency band). To avoid the interference between mobile WiMAX and the existing system, it is assumed that mobile WiMAX is deployed in this frequency band, the most important thing is to do the analysis on co-existence problem.

Some research results show that the interference between these two systems is very small and no additional protection is requierd when the BSs of the two systems are not co-sited. When the BSs of the two systems are co-sited, the inter-system interference except in WiMAX UL is negligible. The WiMAX UL capacity loss due to GSM BS can be alleviated to a satisfied level through increasing either ACIR (Adjacent Channel Interference Ratio) or antenna isolation. If the method of increasing ACIR is used, the recommended value is 85dB. On the other hand, if the method of increasing antenna isolation is used, the recommended value is about 60dB. Furthermore, these two methods can be used simultaneously and the required values for ACIR and antenna isolation are lower than the above-mentioned value.

My MS Antenna Design for 3.5GHz WiMAX..

As a new system, WiMAX has it special requirements and constraints.

• It operates at high frequency (2.5/3.5/5.5GHz)-> higher signal attenuation
• Deployment needs wide transmission bandwidth (5/10MHz)->high data rates per user
• It has the need to use high-level modulation (up to 64QAM)-> high capacity and high data rate per user
• it has the dimensioning with stringent indoor penetration requirements
• According to these requirements, I designed a patch antenna working at one of the possible WiMAX frequency, i.e. 3.5GHz. The design specification is as follows:

• 50Ω transmission line
• Substrate: FR4 (Flame Resistant 4)
  -Composite of a resin epoxy reinforced with a woven fiberglass mat
  -Єr = 4.4
  -tanδ = 0.01 @ 10GHz
  -Less lossy at high frequencies
  -Absorb less moisture
  -Greater strength and stiffness
  -Highly flame resistant compared to its less costly counterpart
  -Ultra high vacuum compatible


• Height of dielectric substrate (h): 1.5mm
  -for usage in cellular phones, it is essential that the antenna is not bulky.
• Patch
  -Conducting material such as copper or gold
  -Take rectangular shape as example
  -Large bandwidth and gain

The design procedure is as follows.

Other parameters are calculated as below.

Based on the above parameters, we get the following patch antenna.
This patch antenna has its advantages and disadvantages.

Advantages:

• Light weight and low volume
• Low profile planar configuration which can be easily made conformal to host surface
• Low fabrication cost, hence can be manufactured in large quantities
• Supports both, linear as well as circular polarization
• Can be easily integrated with microwave integrated circuits
• Capable of dual and triple frequency operations
• Mechanically robust when mounted on rigid surfaces

Disadvantages:

• Narrow bandwidth
• Low efficiency
• Low gain
• Extraneous radiation from feeds and junctions
• Poor end fire radiator except tapered slot antennas
• Low power handling capacity
• Surface wave excitation

Base Station Antenna Design in WiMAX system..

To increase the capacity and coverage in broadband data communication according to the IEEE 802.16e WiMAX standard, intelligent base station antenna with beam- and nullsteering over a full circle is developed and optimised.

Conventional base station antennas in existing operational systems are either omnidirectional or sectorized. The greater part of the transmitted signal power is radiated into directions other than toward the specific user. This causes interference, reduces efficiency and the range of coverage. Especially in new broadband services as WiMAX, where the user front-end is very simple, it becomes necessary to provide every user with a specific beam offering enough gain to increase the range. It is also important to reduce interference by other users or services by means of beam forming in a way, that either the side lobe attenuation of the base station antenna array as a whole is optimised or by null steering. In rural areas a whole 360 degrees coverage around the base station is desired. This leads to the solution introduced here of circular antenna arrays, a setup which can be used for direction finding.

The antenna array consists of 8 vertical dipoles equally spaced on a ring with diameter d. This building block is vertically stacked many times to achieve enough gain in the horisontal plane. The number of side lobes and the side lobe attenuation depends on the radio d/λ which is ranged in 1/2 and 3/2. It is possible to provide m different and imdependent beams in m directions concurrently. Each dipole is fed by an amplitude and phase actuator and isolated power dividers. In principle this can also be achieved by means of a digital signal processor.

With the circular array of vertical dipoles it is possible to steer the beam in the direction of any user and to provide an optimal side lobe attenuation for m different directions simultaneously. The number of coexistent beams is only limited in practice by the capabilities of the power dividers.

It is also possible to provide a full nullsteering in every direction around the base station. This can be done by phase shifters and attenuators in the RF-region or by DSP after linear down conversion. The results are achieved by the numerical EM-solver FEKO.

With this antenna array it is possible to enhance either the coverage in rural areas or to enhance the capacity of the network.

Antenna & Interference in WiMAX

By utilizing AAS and beam steering technologies, WiMAX overcomes interference while boosting range and throughput.

Adaptive Antenna Systems (AAS) use beam-forming technologies to focus the wireless beam between the base station and the subscriber. This reduces the possibility of interference from other broadcasters as the beam runs straight between the two points.

The potential spectrum for WiMAX is 2.5/3.5/5.5 GHz among which there may be a lot of interference. One of the simplest remedies to interference is to simply change frequencies to avoid the frequency where interference occurs. Dynamic frequency selection (DFS) does just that. A DFS radio sniffs the airwaves to determine where interference does not occur and selects the open frequency to avoid the frequencies where interference occurs.

Multiple in and multiple out (MIMO) antenna systems work on the same principle. With multiple transmitters and receivers built into the antenna, the transmitter and receiver can coordinate to move to an open frequency if/when interference occurs.

Software defined radios (SDR) use the same strategy to avoid interference. As they are software and not hardware defined, they have the flexibility to dynamically shift frequencies to move away from a congested frequency to an open channel.