Wimax Implementation On Gnu Radio Platform Information Technology Essay

From the last few decades, the telecommunication industries are competing with each other and the existing technology to improve them from wired to wireless and provides the subscriber with exceptional quality of service. As the issue arises, the technology like WiMAX is deployed by many telecommunication industries. Since broadband wireless internet connection has become the backbone for almost all the business environment, thus WiMAX can only be the best choice ever. WiMAX, also known as IEEE 802.16 standard is the latest technology that offers high throughput for both fixed and mobile stations.

The purpose of this thesis is to implement the basic features of WiMAX OFDM physical layer based on IEEE 802.16-2004 on GNU Radio platform. Since the project is based on Software Defined Radio (SDR), the goal of this thesis is to transmit and receive a data via USRP connected on the PC. As OFDM is very flexible transmission scheme because it supports different modulation methods. For this purpose, the project is based on BPSK modulation. The project is designed on GNU Radio Companion which helps to provide real time simulation to analyse all the necessary parameters like bandwidth, transmission rate, bit rate, Bit Error Rate (BER) etc. Thus the WiMAX transmitter and receiver are designed to transmit and receive data from the antenna of the USRP.

The thesis gives an overview of the software defined radio (SDR), its application and advantage. The thesis also reflects the concept of WiMAX standard and the performance of WiMAX transmitter and receiver. The result of the simulation clearly helps to understand the basic concept of WiMAX transmission and reception patterns.

Introduction

The wireless technology are emerging technology that is leading the current business market and making lots of profit within the telecommunication industries. Today there are numerous wireless technologies used for various applications. Some of the most widely applicable wireless communication technologies are listed below:

AM/FM. (Voice transmission)

Infrared. (Data transmission, Low speed, LOS required)

Bluetooth. (V2.0 faster than infrared, NLOS, Frequency hopping)

ZigBee. (Similar to Bluetooth with greater range and throughput)

Wi-Fi.(IEEE 802.11 WLAN network, OFDM,TDM)

WiMAX. (IEEE 802.16 WMAN Network, OFDM,OFDMA)

Wireless radio transmissions are based on transmission of radio waves that propagates through air. Radio waves that lie between the frequency ranges of 30 MHz to 20 GHz are generally used for data transmission. The frequency range that is lower than 30 MHz generally support data transmission/communication, but these frequency bands are typically used for voice transmission over long distance, example: Frequency Modulation (FM), Amplitude Modulation (AM) radio broadcasting as these waves reflect on the ionosphere surface of the Earth’s atmosphere to extend the communication. Radio waves that propagate over 20 GHz frequency band cannot be used for long-distance communication because it may easily get contaminated by the moisture present in the atmosphere.

Due to the higher demand and utilization of digital network, the telecommunication industries are forced to design the new communication network with higher capacity and load. These industries are changing themselves due to the demand for the services to provide in greater range and quality such as voice and video conferencing, online application, multimedia content etc. The dependency on computer network these days are far greater than before and the internet has led to the higher demand for the connection to be provided on the fly, which in turns leads to the increase in the needs for higher capacity and reliability broadband wireless telecommunication systems.

Availability of Broadband introduces high performance connectivity to over almost all of the internet users’ worldwide, thus introducing new wireless broadband standards and technologies that will rapidly full fill the need of wireless coverage. Digital wireless communications are emerging technologies that are facing stunning expansion during the last few decades. The new method of obtaining high capacity wireless network is because of none other than the large application of cellular mobile technology, WLAN (Wireless Local Area Network) and the exponential growth of Internet. [1].

Worldwide Interoperability for Microwave Access, known as WiMAX, is a wireless networking standard that is specially designed for addressing interoperability based on IEEE 802.16 products. WiMAX also defines a wireless metropolitan area network (WMAN), where the users get connected to the main station of broadband wireless provider. It incorporates the feature of both line of sight (LOS) and non-line of sight (NLOS) communication and is alternative technology deployed to replace cables, DSL or T1, E1 etc. One of the most advantageous features of WiMAX based product is that, any products based on WiMAX technology can be shared with some other technologies that provide broadband access and can be implemented in most of the possible areas. The figure below shows the deployment of WiMAX.

It is believed that soon WiMAX will replace all other broadband connection across the globe and is most suitable for the places where it is difficult to deploy other technologies like DSL and cable and is the best choice for the solution of last mile internet access on the go. On the other hand, where wired network are more sophisticated and costly for the maintenance, WiMAX again becomes the best choice for implementation. In this way, with the help of WiMAX, rural, urban areas can easily gets connected to the developed areas or city. WiMAX itself can even be used to deliver backhaul for mobile carrier, universities, and Wi-Fi hot-spots. WiMAX offers a best solution for such challenge as it is cost-effective, easily deployable, high data rate and more above these is its feature of mobility.

WiMAX has become one of the largest competitors to 3G cellular systems and the mobile data application which can be achieved by IEEE 082.16e is the highest data rate as compared to other technologies till date. Although there is another emerging technology named 3G LTE which is believed to be one of the serious competitors to WiMAX in near future. More detail comparison of WiMAX with other wireless technologies are discussed in later chapters.

Digital modulation:

Digital modulation is a type of modulation scheme that transforms digital signals into waveform that is suitable for the transmission channel. Digital modulation can be divided into two major parts. One of them uses a constant amplitude carrier and the information is carried out as the phase of frequency varies, such as FSK, PSK. The other one is known as amplitude shift keying that carries information on the variation of carrier amplitude.

Different modulation schemes are being used these days for effective wireless communication. From the fast few years the entire digital modulation scheme has transacted from simple amplitude modulation (AM) or frequency modulation (FM) to digital techniques like QPSK, FSK, PSK, MSK, QAM etc.

Objective:

The main objective of this thesis is to study the OFDM physical layer and implement the WiMAX transmitter and receiver with basic parameters required for transmitting and receiving the OFDM signal using the SDR (Software Defined Radio). The detail study of SDR (Software Defined Radio) is discussed in later chapter.

Structure of thesis:

Chapter 1: Deals with the introduction of all the necessary backbone required for the thesis.

Chapter 2: Describes the fundamentals of WiMAX and OFDM, their characteristics, advantages and disadvantages.

Chapter 3: Describes the approach that is used for the simulation i.e. SDR (Software Defined Radio).

Chapter 4: Simulation design.

Chapter 2

IEEE 802.16 (The WiMAX standard):

The WiMAX stands for Worldwide Interoperability for Microwave Access. WiMAX can be used as a wireless metropolitan area network (Wireless MAN) technology to connect with the IEEE 802.11 standard (also known as Wi-Fi) hot spots to the Internet so as to provide a wireless extension to cable and DSL for long distance broadband access. IEEE 802.16 has a service range of up to 30 miles which allows users to connect directly with the base station without direct line of sight requirement. This technology provides shared data rates of up to 70 Mbps, which can be considered to be enough bandwidth to support more than 50 businesses running simultaneously and supports more than thousand homes that are running at 1-Mbps DSL connectivity as well. The initial WiMAX standard, IEEE 802.16 operates in the frequency range of 10- to 66-GHz. Later 802.16a added support to operate in the frequency range of 2- to 11-GHz, for which most of the parts has already been unlicensed internationally, and the requirement of domestic license for few of them is still remaining to acquire. Because of licensing issue most of the business will probably deploy 802.16a standard. The WiMAX is an enhanced and improved version and is one of the latest technologies that will overlap the limitations of the 802.11 standard by providing extended bandwidth, range and security. In some circumstances, WiMAX is often aimed to provide the connectivity between network endpoints without having the requirement of direct line of sight. In most of the cases as we know that the spectrum that falls less than 5 to 6 GHz is needed to provide reasonable Non-Line of Sight performance and cost effectiveness for point-to-multipoint deployments. WiMAX makes an efficient use of multipath signals without altering the laws of physics. The data rate that is supported by the 802.11 can be easily supported by 802.16, but the only issue that arises is about the interference which is lessened. WiMAX can operate both on licensed as well as non-licensed frequencies that provide the suitable environment of deployment for the wireless service providers. For the deployment of the WiMAX technology, two main parts are required,

WiMAX tower

WiMAX receiver

A WiMAX tower is similar to the tower of cell phone, which transmits signal in all direction. The receiver that falls within the range can easily gets connected with or without the need of line of sight requirement. It is assumed that a single WiMAX tower can provide a very large coverage area of 3000 Sq mi which is equivalent to 8000 sq km.

A WiMAX receiver is similar to that of cell phone that have an embedded antenna or it may be of small piece of box, PCMCIA (Personal computer memory card international association) card that can easily be plugged in to the laptop or may be built in to the laptop in the same way as Wi-Fi receiver is.

A WiMAX tower station has a direct wired internet connection of very high bandwidth. One WiMAX tower can be easily connected to another WiMAX tower using a LoS microwave link. Because of this feature of connecting one WiMAX tower with another WiMAX tower which is also referred to as a backhaul, allows WiMAX provider to cover very large area in remote places where the other service provider have not been able to provide wired connection like DSL, Cable, T1 etc. A typical scenario of WiMAX transmitter and receiver is shown in the fig below.

A WiMAX operation comprises a WiMAX Base Station that provides coverage for entire metropolitan area. Edge network and WiMAX base station can be connected by wireless point-to-point link or by fibre optics link whatever available. WiMAX with point to multipoint wireless connection is effective method for providing last mile broadband access which is not only cost-effective but have high bandwidth to support numerous users at a time. Fixed WiMAX service can be provided to the subscriber by means of end devices (receiver) that are normally mounted on the roof or can either be indoor units. In case of providing service for residential user, RJ-45 or RJ-11 connections are typically included to deliver high speed internet connection without requiring any other additional devices except laptop (PC) or telephone. In order to provide service for business types, T1/E1 interface along with 10/100 Base T Ethernet connection would be desirable. Wireless distribution system can be enabled within the building periphery by means of wireless LAN (Wi-Fi), once the WiMAX terminal gets combined with the existing wireless router. Because of limited spectrum in the lower frequency bands, WiMAX will have limited capacity and will require the alteration of Base Station at a distance of 2 to 3 km. However in the remote areas with low density population, WiMAX can take full advantage and can provide full coverage up to 75 sq km in 3.5 GHz frequency band.

The WiMAX quality of service (QoS) is accomplished as it is designed to support variety of traffic such as applications that require very high data rate example: voice and video streaming, applications that require low data rate example: web surfing. Network like WiMAX cannot operate without certain quality of service. While running applications that require very high or low data rate some delays can be acceptable but introduction of too much delay makes application useless. Thus according to IEEE 802.16 group an acceptable delay for VoIP is considered between 120 ms – 150 ms. Keeping all this in mind IEEE 802.16 is designed to be flexible enough and efficient to respond to the end user applications with varied bandwidth and latency requirements.

OFDM-256 PHY used in fixed WiMAX could not be used in mobile WiMAX 802.16e as it is specially designed to address mobility so as to meet the requirement for mobile applications. Since the fixed and mobile WiMAX physical layer are fundamentally incompatible and these two versions will be used for different applications. More detail study of WiMAX physical layer is included in later topic. Transition of IEEE 802.16 to IEEE 802.16e-2005 is tabulated below.

Standard

802.16 802.16-2004

802.16e-2005

Year

2001

2004

2005

Frequency band

10GHZ-66GHz

2GHz-11GHz

2GHz-11GHz for fixed.

2GHz-6GHz for mobile.

Application

Fixed LOS

Fixed NLOS

Fixed and mobile NLOS

MAC Architecture

Point-to-multipoint, mesh

Transmission scheme

Single carrier

Single carrier, 256 OFDM or 2048 OFDM

Single carrier, 256 OFDM or scalable OFDM with 128, 512, 1024 or 2048 subcarriers.

Modulation

QPSK, 16 QAM, 64 QAM.

Gross data rate

32Mbps-134.4Mbps

1Mbps-75Mbps

Multiplexing

Burst TDM/TDMA

Burst TDM/TDMA/OFDMA

Duplexing

TDD and FDD

Channel-Bandwidths

20 MHz, 25 MHz, 28 MHz

1.75MHz, 3.5MHz, 7MHz, 14 MHz, 1.25 MHz, 5MHz, 10MHz, 15MHz, 8.75 MHz

1.75MHz, 3.5MHz, 7MHz, 14MHz, 1.25 MHz, 5MHz, 10 MHz, 15 MHz, 8.75 MHz

Air-interface designation

Wireless MAN-SC

WirelessMAN-SCa

WirelessMAN-OFDM

WirelessMAN-OFDMA

WirelessHUMAN

WirelessMAN-SCa

WirelessMAN-OFDM

WirelessMAN-OFDMA

WirelessHUMAN

Implementation

none

256-OFDM for Fixed.

Scalable OFDMA for Mobile.

Relationship with other wireless standard:

WiMAX Vs. 3G LTE

The new WiMAX standard delivers the downlink speed of more than 128 Mbps and uplink speed of 56 Mbps in 20 MHz bandwidth. WiMAX update IEEE 802.16m is expected to offer bandwidth of at least of 1 Gbps for fixed and 100 Mbps for mobile users. The key strength to choose WiMAX is that it uses the approach similar to that of cell phone thus no line of sight is required. The signal broadcasted by the WiMAX is not prone to interference, it is more secure with good quality of service and the most important is its reliability. The WiMAX network includes two key components: a base station to transmit the wireless signal and the subscriber that receives the signal on WiMAX enabled devices. The Mobile WiMAX standard incorporates the Orthogonal Frequency Division Multiple Access (OFDMA) and Multiple Input/Multiple Output (MIMO) smart antenna technology. These technologies help to provide more data into the available airwaves to increase throughput and/or coverage. MIMO is particularly beneficial in high interference environments, like urban centres.

3G LTE on the other hand is a GSM technology (UMTS Cellular technology) that is currently used by the carriers to provide 3G mobile broadband. It incorporates the use of same technology as in WiMAX i.e. OFDMA/ MIMO and SC-FDMA technology. It delivers the downlink speed of 100 Mbps and uplink speed of 50 Mbps in 20 MHz bandwidth. It supports at least 200 active users in every 5 MHz cell. LTE-advanced is expected to offer 1 Gbps for fixed and 100 Mbps for mobile users. HSPA (High Speed Packet Access) which is a combination of HSDPA, HSUPA and HSPA+ are now being deployed. 3G LTE is generally known as 3.99G as it is does not offers full 4G functionality. It uses system architecture Evolution (SAE) so as to reduce the latency time and to route the data to its destination directly.

As it is seen that both WiMAX and 3G LTE are similar technologies are still competing to stand. In case of business environment, WiMAX has already been implemented and is in market where as LTE is still in testing phase. The operator can establish WiMAX network with very low cost as compared to 3G LTE. 3G LTE consumes less power than WiMAX. Latency is one if the key factor in online services like online gaming and videoconferencing, in case of WiMAX is 50 ms but for LTE is only 10 ms. 3G LTE can be easily upgraded to 4G as it is fully integrated with similar infrastructure whereas WiMAX has still not seen any sort of upgrade, so telecom industry can easily set-up the 3G LTE technology without concerning the future development of LTE. In terms of mobility, a mobile target is required with a speed lower than 120 km/h in case of WiMAX but LTE can cope up to 350 km/h.

WiMAX Vs. Wi-Fi

IEEE 802.11 which is also known as Wi-Fi (Wireless fidelity) or WLAN is a wireless standard capable of offering data rate up to 54 Mbps at 5.2 GHz frequency band. IEEE 802.11b which operates in the frequency band of 2.4 GHz supports data rate of up to 11 Mbps. These technologies provide a coverage area of 100 m and have a fixed channel bandwidth of 20 MHz.

IEEE 802.16 standard is a solution for last mile wireless broadband internet access that Wi-Fi has not been able to provide. WiMAX architecture is specially designed for metropolitan area network (MAN) for which the base station of WiMAX will be able to provide access to thousands of subscribers. Wi-Fi on the other hand having very less coverage area provides only local area network (LAN). WiMAX installation requires very high cost as compared to Wi-Fi thus Wi-Fi becomes more suitable for those who cannot afford things at high cost. There can be numerous similarities and dissimilarities between Wi-Fi and WiMAX, however WiMAX is considered to be the birth of Wi-Fi with very high data rate and range to provide exceptional quality of service.

A more detailed comparison of WiMAX with other wireless and cellular technology is tabulated below.

Wi-Fi

WiMAX

UMTS

HSDPA

Standard

802.11

802.16

Channel width

20 MHz

Variable

20 MHz

Variable

28 MHZ

Fixed

5 MHz

Spectrum

2.4 – 5.2 HGz

2-11 GHz

10-66 GHz

2 GHz

Data rate

2-54 Mbps

70 Mbps

240 Mbps

1-14 Mbps

Range

100 m

1-7 Km

12-15 Km

50 Km

multiplexing

TDM

FDM/ TDM

FDM/TDM

FDM

Transmission

OFDM

OFDM/ OFDMA

WCDMA

Mobility

Pedestrian

Vehicular (802.16e)

Vehicular

Advantages

Throughput and costs.

Throughput and range.

Mobility and Range.

Disadvantages

Short range.

Interference issues, synchronization issue.

Low data rate and expensive.

Rate

Wi-Fi

WiMAX

UMTS

Mobility

Fig: – Comparison with other wireless standard.

WiMAX Technical overview

The IEEE 802.16 group was formed in 1998 to develop an air-interface standard for wireless broad-band. The group’s initially intended to develop of a line-of-sight based point-to-multipoint wireless broadband system that operates in the 10GHz-66GHz millimetre wave band. Later on the IEEE 802.16 group produced 802.16a to include non-line-of-sight (NLOS) applications in the 2GHZ – 11 GHz band, using an orthogonal frequency division multiplexing (OFDM) – based physical layer. The revisions made further resulted a new standard in 2004, called IEEE802.16-2004, which replaces the entire previous version and formed the basis for the first WiMAX solution. Further the WiMAX is enhanced in various aspects of signal processing and transmission techniques.

Starting from IEEE 802.16 up to IEEE 802.16e-2005 a number of enhancements have been made, it is discussed (tabulated in table 1). From this we can conclude that IEEE 802.16 is a bunch of standards that can be deployed depending on the requirements, it can be achieved by defining a limited number of system profiles and certification profiles. Currently, the WiMAX forum has two different system profiles: one based of IEEE 802.16-2004 i.e. fixed system profile and other one based of IEEE 802.16e-2005 i.e. mobility system profile. The WiMAX forum has defined five fixed certification profiles and fourteen mobility profiles so far. To date, there are two fixed WiMAX profile against which equipment have been certified.

With the completion of the IEEE 802.16e-2005 standard, the WiMAX group has advanced their step towards developing mobile WiMAX system profile based on the newer profile. This uses scalable OFDMA as the physical layer. It is also found that the current mobility certification profiles are based on TDD. Although TDD is preferred more, but FDD profile may be needed in the future to comply with regulatory pairing and interoperator coexistence requirements in certain bands.

Air interface for IEEE 802.16-2004 specification that operates on frequency band of 2-11 GHz is defined by the WiMAX standard. This air interface defines the medium access control (MAC) and physical layer (PHY) of WiMAX.

Medium Access Control (MAC) layer

The IEEE 802.16 MAC was specially designed for point-to-multipoint BWA application based on CSMA/CA scheme. The WiMAX MAC layer which is situated above the PHY layer is one of the major parts that play a vital role for providing an interface between the transport layer and physical layer. It takes packets called MAC service data units, organize into MAC protocol data unit and transfer to the physical layer for wireless transmission. The reverse process is done in the receiver end. The IEEE 802.16-2004 and IEEE 802.16e-2005 MAC layer is designed to have various sub layers to interface with different higher layer protocols like internet protocol, Ethernet, ATM TDM voice, etc.

Due to the requirement of services in different environment the MAC layer is designed to support multiple physical layer specification and services. Since the base station is responsible for controlling different independent sectors, MAC layer works with point to multipoint network topology. MAC layer supports various algorithms, among them Access and bandwidth allocation algorithms controls numerous terminals that may be shared by numerous users. Thus the MAC protocol is responsible for defining the transmission between base station (BS) and a subscriber station (SS) on the channel. MAC protocol in the case of downstream channel is quite simple that uses time division multiplexing (TDM) to multiplex the data whereas in case of upstream channel MAC protocol uses time division multiple access (TDMA) technique to ensure the efficient use of the bandwidth as there will be multiple subscriber stations competing to access the medium. There will be multiple users running various applications independently and thus the service is varied according to the number of users that uses voice or video conferencing, web surfing etc. to support these variety of services MAC layer accommodates both continuous and bursty traffic by ensuring the amount of data rate and delay required by each services.

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