Pervasive wireless networks

Introduction

Wireless networks have been used for communication for decades now. Wireless networks  not only provide us with location independence but also ease of access. Wireless communication has evolved to a very large extent in past few decades. In today’s world we see many forms of wireless communication networks viz. Cellular networks, WiFi networks, and personal area networks. Today the need for high speed, low cost data connectivity is growing day by day.

Wireless networks generations 

Wireless communication devices have been evolved in many generations

• First generation (1G) – Transmission of only voice
• Second generation (2G) – Voice as well as data transmission. The 2.5G as well as 2.5G+ are enhancements which could support higher data transmission rates.
• Third generation (3G) – More transmission rates including transmission of voice, data and multimedia streams.

Communication standards

Long range communication –

Wireless communication devices such as mobile phones use the following standards for communication

• GSM
• CDMA

GSM – GSM (Global system for mobile communication) was developed in 1982 in Europe. GSM support the data rate of about 14.4 kbps. Many standards have been derived based on GSM which are explained below.

GSM 900	Found in 1982. Uses FDMA and TDMA for user access of channel. Operate at 890-915 MHz for uplink and 935-960 MHz for downlink. Data rates are 14.4 kbps.
EGSM (Enhanced GSM)	Operate at 880-915MHz for uplink and 925-960 MHz for downlink
GPRS (General packet radio service)	Is a packet oriented service. Uses unused channels in TDMA mode in a GSM network
EDGE (Enhanced data rates for GSM evolution)	Higher data rates upto 48 kbps. The rates can be enhanced upto 384 kbps by coding techniques.

CDMA – CDMA (Code division multiplexing access) is one more mobile standard which started in  1991. CDMA support high speed data rates and is considered 3G. CDMA can transfer voice, data as well as multimedia.

CDMA based standards are explained as follows.

CDMA one	Founded in 1991. Operates at 824-849 MHz. Can transmit along signals from multiple sources and users.
3GPP (Wide CDMA)	Support asynchronous operations. Support 3.84 Mbps chipping rate.
3GPP2	Founded in 2001 Used for voice, multimedia, real time multimedia, circuit and packet switching communication.
UMTS (Universal mobile communication system)	Support both 3GPP, 3GPP2 Data rate of 100 kbps to 2 Mbps. Chipping rate of 3.84 Mbps.

Short range communication –

Although wireless devices use mobile network standards for long range communication the short range communication is facilitated by WPAN & WLAN.

WPAN (Wireless personal area network) – WPAN assist the communication of mobile devices with home computers at short distances.

WPAN use following standards for communication.

1. Bluetooth – Bluetooth IEEE 802.15.1 is one of the standard used by WPAN which operate at the frequency of 2.4 GHz. It is identical to IEEE 802.11b WLAN standard. It provides short distance mobile communication with a data rate of 1 Mbps. Examples of such transmission are mobile phone headset, hands free etc. 
2. ZigBee – IEEE 802.15.4 standard used by WPAN is called as ZigBee. ZigBee is used in lower transmitting power systems. It has lower network joining latency as compared to Bluetooth. It provides automation and remote controls up to range of 70 m. The data rates supported by ZigBee are 250kbps, 40kbps & 20kbps with a spectra 2.4 GHz, 902 to 928 MHz & 868 to 870 MHz.

WLAN (Wireless Local Area Network) & Internet access – WLAN facilitates the communication between mobile and internet. WLAN is WiFi (Wireless Fidelity) based service. WLAN uses the following set of standards for communication.

IEEE 802.11a	It support infrastructure based architecture as well as mobile ad hoc network. It uses OFDM modulation. The data rates supports are from 54 kbps to few Mbps.
IEEE 802.11b	It operates at 54 Mbps and 2.4 GHz. Modulation is DSSS/FHSS. It also support distance wireless networking using Bluetooth It provides protected WiFi access Data rates are 1 Mbps (Bluetooth), 2 Mbps, 5.5 Mbps, 11 Mbps and 54 Mbps(HIPERLAN 2).
IEEE 802.11g	Operates at 54 Mbps and 2.4 GHz. Support many new Bluetooth applications and compatible with 802.11b. Uses DSSS modulation in place of OFDMA.
IEEE 802.11i	Provides AES (Advance encryption standard) & DES (Data encryption standard) security standards.

Security – Security is one of the main areas of concern in the wireless network communication. Some of the main security issues are

• Security of the data transmitted from one point to other.
• Non repudiation of the data
• Authentication

Authentication – Authentication has been an important issue in security. For authentication in wireless networks use secrecy code which is calculated using the 128 bit random number given by the base station. Then authentication code is calculated. This is sent back to base station which is compared with number in the database if the number matches the device is authenticated.

Security of data – For security of data the wireless devices uses the cryptography algorithms which encrypt the data in some other unreadable format. There are two categories of algorithms Symmetric and Asymmetric.