Enhanced Data rates for Global Evolution

The first stepping stone in migration path to third generation wireless mobile services (3G) is the General Packet Radio Services, GPRS, a packet-switched technology that delivers speeds of up to 115kbps. If GPRS is already in place, Enhanced Data rates for Global Evolution (EDGE) technology is most effective as the second stepping stone that gives a low impact migration. Only software upgrades and EDGE plug-in transceiver units are needed. The approach protects operators' investments by allowing them to reuse their existing network equipment and radio systems.

The EDGE technology will enable GSM and TDMA operators to deliver third-generation mobile multimedia services using existing network frequencies, bandwidth, carrier structure and cell planning process. By using a more efficient air-modulation technology optimized for data communications, EDGE increases end-user data rates up to 384kbit/s and potentially higher in good-quality radio environments

Vertical Cavity surface Emission Lasers

Vertical Cavity surface Emission Lasers (VCSEL) are lasers that emit light from their surface in contrast with regular ‘edge emitters’. Also they have got a vertical cavity , as the name suggests, which enables surface emission.”Vixels” , as they are commonly called ,have several superior characteristics compared to their edge emitting counter parts.

VCSEL – Semiconductor micro laser diodes which emit light perpendicular to their PN junction in a cylindrical beam vertically from the surface of a fabricated wafer and feature circular low divergence beam

Earliest reported in 1965 by Melngailis

VCSEL was first demonstrated in 1979 at Tokyo Institute of Technology

Epitaxial mirrors for GaAs/ AlGaAs VCSELs

pioneered in 1983

Distributed Bragg Reflection

If layers of alternating semiconductors are stacked periodically , each layer having a thickness

λo n , the reflections from each of the boundaries will be added in phase to produce a large reflectivity

Brag reflection condition

Periodicity of cladding layer is chosen so that

n1d1 + n2d2 = λo/2

n1 , n2 refractive indices

d1 , d2 thickness of layer

λo free space wavelength of the optical beam

Epitaxial growth of VCSEL

There are two methods

1 . Molecular beam epitaxy ( MBE )

2 . Metal Organic Vapour Phase Epitaxy (MOVPE)

Inverse Multiplexing over ATM

Local Area Networks are now being used to transport voice and video traffic together with traditional data traffic that they have already supported. And in the case of voice and video applications, not only is these is a need for more bandwidth, but there is also a need for guaranteed levels of receive because these applications are very sensitive to latency and delay.

Inverse multiplexing can be proved as technology that overcomes the bandwidth gap that exists between LAN and WAN. Inverse multiplexing is exactly the opposite of traditional multiplexing. In traditional multiplexing, multiple streams of data are combined into one single but larger data pipe, where as inverse multiplexing combines multiple circuits into single logical data pipe.

Asynchronous Transfer Mode (ATM) has compelling business as a WAN technology and is on a steep growth curve both in public carrier networks and in private organisations with requirements for networking video, voice and data traffic.

Inverse multiplexing over ATM (IMA) is a breakthrough standard that enables ‘right sizing and right pricing of enterprise access solutions for organisations with low to mid range WAN traffic requirements and offers the benefits of ATM’s quality of service and statistical bandwidth optimisation capabilities. IMA divides an aggregate stream ATM cells across multiple WAN links on a cell by cell basis and hence the name inverse-multiplexing. In combination with ATM, IMA simplifies and reduces WAN cost of ownership.