2G - Mobile Access
Second Generation networks, often referred to as PCS (Personal Communications Services), have faced a number of issues. One of those issues has been the lack of interoperability between 2G or PCS networks. This problem lies in the fact that there are actually multiple standards for 2G. 2G - in and of itself, is not formally considered a standard by the ITU (International Telecommunications Union). The three most common 2G standards are cdmaOne (IS-95), GSM, and TDMA (IS-136). Each of these digital standards can operate in the same PCS frequency range of 1.9GHz. However, each utilizes a different Radio Technology and Modulation Scheme, which are characteristics of the standard. Therefore, the lack of interoperability in 2G occurs because of lack of standardization.

2.5G - Mobile Access
Using Motorola's iDEN (Integrated Digital Enhanced Network) as a model, 2.5G networks were designed to thrive where traditional cellular networks fell short. iDEN technology is based on Motorola's SMR (Specialized Mobile Radio) technology. Although, traditional SMR technology has been around for quite some time, "Enhanced" SMR (i.e. ESMR) is digital, providing users with Integrated Services. These Integrated Services includes: Enhanced Dispatch (Two-way Radio) operating in the 800MHz and 900MHz frequency range; Inter-connect or Digital Cellular which uses TDMA (Time Division Multiple Access) technology; Short Messaging Services that include IVR (Interactive Voice Response) and TAP (Telocator Alphanumeric Protocol), Voice-Mail Notification Services, E-Mail Notification Services, and FAX capabilities using IWF (Inter-working Function). However, one of the issues with iDEN is its limited data transmission speeds. Future iDEN networks could potentially address this problem with bandwidth modifications (i.e. WiDEN).

3G - Mobile Access
Third Generation wireless services are currently being deployed successfully in the 1.9 GHz and 2.1 GHz frequency range. However, one of the greatest threats to the survival of 3G lies in its lack of interoperability between “Operating Modes”. Examples of 3G Operating Modes include W-CDMA, and CDMA2000. All of the 3G Operating Modes are associated with the 3G standard. This standard is called IMT-2000 (International Mobile Telecommunications 2000), and was defined by the ITU (International Telecommunications Union) in 1999.

The ITU has defined five (5) separate Operating Modes: W-CDMA (UMTS), CDMA2000, TD-SCDMA, UWC-136 (i.e. EDGE), and DECT. The first three Operating Modes are based on CDMA technology and the latter two are based on TDMA technology. CDMA2000 and W-CDMA (UMTS) are the most widely used - with CDMA2000 being the most dominant. According to 3G-Today (2004), there were a total of 103 commercially deployed 3G networks in over 46 countries (3G Today, 2004) by 2004. Presently, only one country – China, has decided to deploy a network that uses TD-SCDMA. According to the TD-SCDMA Forum (2004), China’s TD-SCDMA network was scheduled to be deployed commercially in 2005 (TD-SCDMA Forum, 2004). Today, only two of the five 3G Operating Modes are commercially in use - CDMA2000 and W-CDMA. This means that interoperability within 3G networks is limited to two operating modes. However, this remains an issue for both consumers and Service Providers – especially from a global perspective since CDMA2000 and W-CDMA use different Radio Transmission Technologies that are not inter-operable. If the goal for 3G was standardization (i.e. ITU-2000), then it has failed to meet this goal.

There are four Radio Transmission Technologies (RTT) associated with Operating Mode CDMA-2000. These include: 1xRTT (1.25MHz Evolution Radio Transmission Technology), 3xRTT (5MHz Evolution Radio Transmission Technology), EV-DO (Evolution Data Only), and EV-DV (Evolution Data & Voice). Only two of these are commercially available – 1xRTT and EV-DO. Marek (2003) noted that current CDMA2000 Service Providers who wished to improve their network data rates, could effectively upgrade their 1xRTT networks to EV-DO through software and BTS module upgrades (although EV-DO requires dedicated spectrum). Service Providers can also upgrade their CDMA2000 networks from either 1xRTT or EV-DO to EV-DV. EV-DV does not require dedicated spectrum since the same 1.25 MHz channel can also be used. EV-DV also has faster data rates than EV-DO (Marek, 2003). Thus, although there is intra-operability within the CDMA2000 operating mode, interoperability between operating modes (CDMA2000 and W-CDMA) does not exist and thus, remains an issue for 3G.

802.11 - Fixed Access
One of the issues surrounding the use of 802.11 has also been its lack of interoperability. This has been primarily associated with its use of different frequency bands. In Chart 2, each 802.11 Physical Layer (PHY) represents a different standard. A comparison can be made between 802.11g WiFi (802.11b upgraded) and 802.11a WiFi5 (i.e. at 5GHz) to highlight the issue of standardization. An assumption is sometimes made that the two standards are inter-operable because they can theoretically achieve the same data rate - 54 Mbps. However, although both standards can operate at the same data rate (theoretically), they don’t share the same frequency band. Thus, interoperability between 802.11b/g and 802.11a is not possible. 802.11a operates in the less congested 5.5 GHz band while 802.11b and 802.11g operate in the unlicensed and very congested 2.4 GHz band. On the other hand, 802.11g is backward compatible with 802.11b since both standards can operate in the same frequency band (i.e. 2.4 GHz), and share a common modulation scheme (i.e. CCK). 802.11n, set to be released in 2009, may address the interoperability issue since it will work in both the 2.4 GHz and 5 GHz frequency bands.

In addition to the interoperability issue associated with incompatible frequency bands, 802.11 standards don’t all use the same modulation schemes. For example, although 802.11b and 802.11g both use multiple modulation schemes (i.e. adaptive modulation), namely OFDM (Orthogonal Frequency Division Multiplexing), CCK (Complementary Code Keying), and PBCC (Packet Binary Convolution Coding) they both share the ability to use CCK (Complementary Code Keying) modulation. This allows interoperability to occur between the two standards. However, 802.11a does not use multiple modulations schemes – it is limited to OFDM. Although the use of OFDM in and of itself is not a bad thing, it does limit 802.11a’s ability to communicate with 802.11b. Note: 802.11n may use OFDM Modulation which could make it compatible with previous OFDM 802.11 devices in the same frequency band. Thus, some efforts are being made to address interoperability issues. However, it’s very clear that lack of standardization and interoperability are significant issues for Fixed Access Technologies such as 802.11.

The chart below, provides a comparison between Fixed Access Technologies: 802.11b, 802.11g, 802.11a, 802.11e, 802.11i, 802.11h, 802.11j, 802.11n, 802.15.1 (Bluetooth), and 802.16d/e (WiMAX). Note: 802.16a (used in the chart) was updated to 802.16d in 2004.

802.16d/e (WiMAX) - Fixed Access & Mobile Access

There are two modes of WiMAX (802.16d-2004 and 802.16e-2005) and each has a different mission although in general, they will serve similar purposes. WiMAX-802.16d, or Fixed WiMAX, is being primed to carry "backbone" traffic for WLAN Hotspots. It is also being promoted as a viable solution for one of the biggest bottlenecks in a telecommunications network - the "last mile". Those who are pushing 802.16d, look to replace the dependence on T1, DSL and Cable and also look to deploy it in areas where there is currently no wire-line infrastructure in place. WiMAX-802.16e, or Mobile WiMAX, is considered a 4G technology and has a different mission. It is being primed as a means to add Mobility to the WLAN/WiMAX network. WiMAX-802.16e could allow for the combined operations of both fixed and mobile wireless in the same frequency bands. WiMAX also has a large following. A Forum was created to address interoperability issues based on the specifications from the 802.16 Task Group. This is called the WiMAX Forum and includes companies such as Intel, Agilent, and Nokia, just to name a few. Note: Intel plans to integrate WiMAX into its mobile chipsets with WiFi. Therefore, expect computers/laptops that will be able to support both WiFi and WiMAX.

The list below contains many of the potential benefits of WiMAX:

1. Designed with QoS (Quality of Service). This means that as we move towards "convergence" (i.e. Voice, Video & Data transmission all within the same network), WiMAX will have the ability to manage bandwidth between multiple applications such as VoIP, high speed data, and streaming video.

2. Designed with NLOS (Non-Line-of-Site) in mind. The original 802.16 standard was designed for frequencies between 10-66 GHz (Line-of-Site environments). The 802.16d standard is designed to operate in the 2-11 GHz frequency range, while 802.16e was designed to operate in the 2-6 GHz range. It will be possible for both 802.16d and 802.16e to operate in NLOS environments. This was achieved because of modulation changes. 802.16d uses three modulation schemes: SC (single carrier), 256-OFDM and OFDMA modulation. 802.16e will use SOFDMA (Scalable Orthogonal Frequency Division Multiple Access). OFDM modulation performs well in NLOS environments and this is one of the reasons why OFDM is so important. Mesh, Beam Forming, and MIMO antenna technology, used in 802.16e, will help to further improve NLOS in WiMAX.

3. Designed to operate in both Licensed & Unlicensed frequency bands. 802.16d can cover a very wide frequency range – 2GHz to 11GHz. 802.16e also covers a wide frequency range, though slightly shorter – 2GHz - 6GHz. Currently, it has the ability to cover three (3) Licensed bands and one (1) Unlicensed band: 2.3 GHz (Licensed); 2.5 GHz (Licensed); 3.5 GHz (Licensed); and 5.8 GHz (Unlicensed). Note: The WiMAX Forum also has plans to add the 700MHz Licensed band to is technology roadmap.

4. Scalability. 802.16 supports multiple channel bandwidths (i.e. Profiles): - For 5.8 GHz Unlicensed - 10 MHz & 20 MHz channels (5MHz for 802.16e) - For 3.5 GHz Licensed - 1.7 MHz, 3.5 MHz, 7 MHz, & 10 MHz channels - For 2.5 GHz Licensed - use 3 MHz & 6 MHz channels

5. Has a very high data rate. Typical channel transmission rates can reach 100Mbps (theoretically) and 70Mbps (15 Mbps for 802.16e). Thus, a single Base Station with 4 Access Units could conceivably deliver 280 Mbps.

6. Works with different packet delivery mechanisms including IPv4, IPv6, Ethernet, and VLAN.

7. Highly secure. 802.16a uses Triple-DES (128 bit) security and RSA (1024-bit)

8. Uses OFDM (Orthogonal Frequency Division Multiplexing) – a very spectrally efficient (~3.7bps/Hz) modulation scheme. OFDM was also chosen over CDMA (Code Division Multiple Access) which is far less spectrally efficiency (~1.6bps/Hz). CDMA modulation techniques (especially Direct Sequence) use PG (Processing Gain) to overcome Co-channel Interference. Therefore, the available bandwidth (i.e. spectrum) has to be larger than the data throughput.

9. Uses a Dynamic Access Method for Media Access Control (MAC). WiMAX-802.16d/e uses TDM/TDMA (i.e. Time Division Multiplex on the Downlink and Time Division Multiple Access on the Uplink) for efficient bandwidth usage. This is a more versatile Access Method than CSMA/CA - a Contention based access method. TDM/TDMA is good for delay-sensitive applications such as Voice & Video and allows for collision-free access to the channel. CSMA/CA does not offer guarantees on delay.

10. 802.16d equipment has a range of up to 30 miles (approximately 3 miles for 802.16e) - far out distancing all other WLAN equipment. With this kind of range, services can be delivered to numerous homes and businesses without having to use multiple APs (Access Points). Note: Advanced antenna technology is also used to facilitate this.

11. Designed to use Spatial-Diversity to enhance performance in Multi-path Fading environments.

12. Designed to use TPC (Transmit Power Control). TPC was also included in standard specifications - 802.11h (Europe) and 802.11j (Japan). TPC allows users that are close to an AP to reduce transmission power in order to reduce interference with other users.

4G - Fixed & Mobile Broadband Access

Fourth Generation Networks will be based on "convergence" and the "Internet Protocol" - IP. We will define 4G as a standard for the transmission of integrated voice, video, and data over a "converged" Mobile Broadband Wireless Access (MBWA) and Fixed Broadband Wireless Access (FBWA) all IP Network (Price, 2004). WiMAX mobility networks or 802.16e networks are considered 4G. The chart below represents a potential migration path towards 4G.