Whitepapers

There has always been a great divide between wealthy, developed nations and poor, underdeveloped ones. This divide spans from economic wealth to social conditions, and it has now reached the communications and information technologies. This is what is now known as the digital divide.

In today’s economy, connecting remote communities through broadband communication is the heart of the digital revolution - and critical to global long-term health and prosperity.

It is believed that bridging the digital divide, and providing communications technologies to remote communities in developing countries can improve the lives of more than 80% of their population.

At the same time, these remote communities have very stringent constraints which make it economically unattractive to connect them. Many government agencies and businesses are left wondering how they can participate and take advantage of the technological advancements which are helping economies in the developed world thrive.

They are now aware that in order for any community to become productive and prosperous, it must first be connected to the rest of the world through these communications technologies.

The traditional approach of extending urban-centric communication infrastructures to remote applications is no longer adequate, as governments and social organizations increasingly focus on providing communications services. Instead, these communities need a remote-centric business-oriented approach.

Technologies such as the Internet, personal computers and wireless telephony allow individuals, businesses, schools and governments to communicate and interact with each other, regardless of geographic limitations.

This paper provides the solutions needed to effectively provide a remote-centric rugged communication solution, while helping business and government executives achieve the highest possible return on their information infrastructure investment.

Applications through information technology (IT) are the driving forces behind every global business operation or government remote community initiative. Today, it is cost prohibitive for businesses and governments to dispatch human resources to collect information in order to make business decisions.

For example, in the energy resources industry, the resource extraction takes place in a remote area or worksite for a defined period of time. However, the business decisions using the information gathered from these remote locations is done in a central office far from the energy resource location. In these situations, the information is required in real-time and becomes critical from the business perspective.

The same concept applies for remote community sensor applications - from environment monitoring to security surveillance. In addition, connecting remote communities through IT networks for social, educational, and information sharing purposes enables huge gains on economic growth and prosperity for the regions, specifically in developing and emerging markets.

There is a high demand for data sharing and integrated communications for making intelligent business decisions and intelligent information sharing. All is required in real-time. Simply stated, a global business or government agency cannot afford to ignore real-time IT communication for remote communities.

Business and government leaders are keenly aware of the cost and importance of the application and the services they support. Not all, however, are aware of the appropriate technologies needed to make cost-effective information access that will reflect a significant business and economic return.

In fact, most remote community projects assume that urban-centric IT infrastructure can be easily extended to their application. In many cases, urban-centric IT infrastructure is an over-kill for remote community applications.

It is also an inadequate fit for the extreme environmental and operating conditions. Choosing the appropriate infrastructure makes a significant business impact on the outcome of the enterprise’s and community projects.

Typically, people relate remote community application to rural community information access. However, the scope also extends to various enterprises providing business transactions to inaccessible communities, such as offshore energy exploration and surveillance services.

In addition, areas of dense population where the terrestrial IT infrastructure is cost prohibitive are also treated as inaccessible remote communities.

Over the past few decades, geographically-challenged remote and rural communities focused on providing basic needs for the population, while proactively, and in many cases, reactively emphasizing the catastrophic health epidemics.

Similarly, global energy resource industries focused on identifying and exploring these resources in various remote locations. These are the intuitive steps that are required by the governments and businesses to establish a social and business base-line.

At the same time, technology has been advancing at a phenomenal pace. Where IT communication was once considered a luxury, it has become a necessity forming the fabric of day-to-day living.

This paper introduces Wireless Voice over Internet Protocol (WVoIP) to enterprises and service providers who want to identify and take advantage of the substantial business opportunities presented by this new technology.

We begin by describing the benefits of standard (wired) VoIP compared to traditional telephony, and the benefits of wireless networking. We point out that by combining VoIP and wireless technologies, companies and organizations can realize the benefits of both.

We go on to introduce some of the important technical aspects of VoIP and WVoIP technology, and describe the main challenges involved in delivering VoIP services—challenges that have been addressed by EION’s own wireless VoIP solutions.

Next, we describe the opportunities created by the new technologies for both enterprises and service providers. Finally, we describe how EION, a leader in wireless IP-based networking, is spearheading the movement to wireless VoIP.

VoIP’s momentum is no doubt part of a larger movement to move all communications to IP-based networks. Driving this move is the fact that delivering everything over IP can be both more economical and allow the delivery of more advanced services.

By now, the benefits of VoIP are probably familiar:

Earlier technical challenges regarding quality of service (QoS) and performance have been addressed, making VoIP a serious alternative to traditional PSTN-based communications systems, and placing VoIP on a level playing field with traditional technologies.

VoIP systems are capable of delivering a substantially richer array of services than PSTN-based networks. In addition to those services with which consumers are currently familiar (such as call display, call waiting, and so on), VoIP supports advanced new services that integrate Internet and telephony applications—such as integrated email and voice mail.

Implementing and maintaining VoIP networks costs much less than traditional PSTN, allowing enterprises with high call volumes to reduce their telecommunications costs, and service providers to add more subscribers and deliver more diverse services for a relatively low rate.

The benefits of wireless communications are also widely recognized:

Wireless networking has allowed many companies, organizations, and even countries to make telephony widely available to both urban and remote rural areas without having to lay cable lines or copper wires.

Wireless technology has advanced to the point where the quality of the services delivered over wireless networks is equivalent to or surpasses that of wired alternatives.

Nonetheless, it is less widely recognized how wireless technology can now be combined with IP-based networking to deliver telephony wirelessly—simultaneously achieving the benefits of both VoIP and wireless technology

Before going on to describe the components of WVoIP, it is important to understand the basic features of VoIP networks and how they differ from PSTN-based networks. With a PSTN (Public Switched Telephone Network), analog voice data is transmitted over copper wires on a network whose parts are owned and controlled by traditional telephone companies (called Incumbent Local Exchange Carriers or Telcos).

With VoIP, voice calls are converted to a digital format that can be transmitted over an IP network (the Internet, a private intranet, or a Virtual Private Network [VPN]). Analog calls can be converted to IP format locally via VoIP gateway devices, transmitted to remote destinations over the Internet for little or no cost, and then enter the remote PSTN via a remote gateway.

Wireless VoIP calls are also transmitted over the Internet, but they rely on wireless access to the Internet—through proprietary wireless protocols, or potentially, WiMAX-based technology.

Just what is OFDM, and what makes it better? To answer this question, we need to review some basic ideas about wireless telecommunications systems, and how OFDM fits into the overall picture.

In what follows, we will review the following concepts needed to understand OFDM; digital messages, carrier waves, modulation and multiplexing. Then we will explain OFDM and why it is used.

Wireless communications systems are used to send messages between two locations using radio waves which travel across free space. Messages of all types (voice, music, image, video, text) are usually converted to digital form and are represented as a stream of 1's and 0's called bits (binary digits).

Voice messages can be represented by about 10,000 bits per second, CD quality music needs about 100,000 bits/sec, and TV quality video messages require about 1,000,000 bits per second, plus or minus. Text messages can be sent at any speed, depending on how long you are willing to wait.

Radio waves are electromagnetic waves used to carry a message over a distance. Thus radio waves are also called a carrier waves. A carrier wave looks like a sine wave, and moves like a train at the speed of light.

The frequency of the carrier wave is the number of times per second that the wave train goes up and down and back up as it moves past you, and is measured in units of cycles per second or Hertz.

Carrier (electromagnetic) waves of different frequencies and wavelengths have different properties. For example, radio waves can travel through walls, but light waves cannot.

Lower frequency waves tend to travel further, and can bend around corners. Higher frequency waves travel more or less only via line of sight. Thus certain parts of the radio spectrum are better suited for certain types of telecommunications.

For indoor wireless communications through walls over a distance of several hundred feet, or outdoor communications over several miles mostly over line of sight with perhaps some trees in the way, carrier frequencies in the range of 1 to 5 GHz (gigahertz or billion cycles per second) are used.

Modulation is the process whereby a carrier wave of a particular frequency is modified or modulated by the message signal, so that the modulated carrier wave can be used to carry the message over a distance. For digital messages (a stream of 1's and 0's), there are three basic kinds of modulation

Amplitude Shift Keying (ASK) (digital AM) in which the amplitude of the carrier wave is modulated in step with the message signal.

Frequency Shift Keying (FSK) (digital FM) in which the frequency of the carrier wave is modulated in step with the message signal.

Phase Shift Keying (PSK) (digital PM) in which the phase of the carrier wave is modulated in step with the message signal.

ASK and PSK may also be used at the same time on one carrier, which is called Quadrature Amplitude Modulation (QAM) or Amplitude/Phase Keying (APK). The receiver is designed to receive the carrier wave, detect these amplitude and phase shifts in the carrier (demodulation), and thus retrieve the digital message.

When a carrier wave is modulated, it is no longer a single frequency but is spread out over a range of frequencies. The bandwidth of the modulated carrier wave is the range from lowest to highest frequency, with the original carrier frequency in the center. The bandwidth is approximately equal to the speed of the digital message, e.g. 10,000 Hz (10 KHz) for voice or 1,000,000 Hz (1 MHz) for video.

OFDM (Orthogonal Frequency Division Multiplexing) is a method of using many carrier waves instead of only one, and using each carrier wave for only part of the message. OFDM is also called multicarrier modulation (MCM) or Discrete Multi-Tone (DMT).

We first describe Multiplexing, then Frequency Division and then Orthogonal. It is important to stress that OFDM is not really a modulation scheme since it does not conflict with other modulation schemes. It is more a coding scheme or a transport scheme.

Orthogonal Frequency Division Multiplexing (OFDM) is a multi carrier transmission technique whose history dates back to the mid1960's. Although, the concept of OFDM has been around for a long time, it has recently been recognized as an excellent method for high speed bidirectional wireless data communication. The first systems using this technology were military HF radio links. Today, this technology is used in broadcast systems such as Asymmetric Digital Subscriber Line (ADSL), European Telecommunications Standard Institute (ETSI) radio (DAB:Digital Audio Broadcasting) and TV (DVBT:Digital Video Broadcasting---Terrestrial) as well as being the proposed technique for wireless LAN standards such as ETSI Hiperlan/2 and IEEE 802.11a. There is also growing interest in using OFDM for the next generation of land mobile communication systems

OFDM efficiently squeezes multiple modulated carriers tightly together reducing the required bandwidth but keeping the modulated signals orthogonal so they do not interfere with each other. Any digital modulation technique can be used on each carrier and different modulation techniques can be used on separate carriers.

The outputs of the modulated carriers are added together before transmission. At the receiver, the modulated carriers must be separated before demodulation. The traditional method of separating the bands is to use filters, which is simply frequency division multiplexing (FDM). Fig. 1 shows a representative power spectrum for three sub channels of a FDM system.

n a classic FDM system, the sub channels are non-orthogonal and must be separated by guard bands to avoid inter channel interference. This results in reduced spectral efficiency.

Another method to achieve frequency separation, but is more spectrally efficient than FDM is to overlap the individual carriers, yet ensuring the carriers are orthogonal is to use the discrete Fourier Transform the (DFT) as part of the modulation and demodulation schemes.

This is where the name orthogonal FDM (OFDM) arises. High speed, fast Fourier transform (FFT) chips are commercially available, making the implementation of the DFT a relatively easy operation.

Fig. 2 shows the spectrum of an OFDM signal with three sub carriers. The main lobe of each carrier lies on the nulls of the other carriers

At the particular sub carrier frequency, there is no interference from any other sub-carrier frequency and hence they are orthogonal. In Fig.2, the sub carriers are 300 Hz apart.

The orthogonal nature of the OFDM sub channels allows them to be overlapped, thereby increasing the spectral tightly efficiency. In other words, as long as orthogonality is maintained, there will be no inter channel interference in an OFDM system. In any real implementation, however, several factors will cause a certain loss in orthogonality.

Designing a system which will minimize these losses therefore becomes a major technical focus. Another advantage to OFDM is its ability to handle the effects of multipath delay spread. In any radio transmission, the channel spectral response is not flat.

It has fades or nulls in the response due to reflections causing cancellation of certain frequencies at the receiver. For narrowband transmissions, if the null in the frequency response occurs at the transmission frequency then the entire signal can be lost.

Multipath delay spread can also lead to inter symbol interference. This is due to a delayed multipath signal presents overlapping with the following symbol. This problem is solved by adding a time domain guard interval to each band OFDM symbol.

Inter carrier interference (ICI) can be width avoided by making the guard interval a cyclic extension of, the OFDM symbol. There are, however, certain negatives associated with this technique.

It is more sensitive to carrier frequency offset and sampling clock mismatch than single carrier systems. Also the nature of the orthogonal encoding leads to high peak to average ratio signals: or in other words, signals with a large dynamic range. This means that only highly linear, low efficiency RF amplifiers can be used.

We present here WOFDM technology, which is less sensitive to inherent OFDM problems such as frequency offset, sample clock offset, phase noise and amplifier non-linearities.

WOFDM is also able to tolerate strong multipath and fast changing selective fading by using a powerful equalization scheme combined with a forward error correction scheme.