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What is DSP?
According to the term, Digital Signal Processing (DSP) refers to electronic processing of signals such as radio, microwaves,  sound, video, image, protocols, control logic and data.
Digital Signal Processors (DSPs) characteristics make them suitable for many purposes like real-time data communication, high-quality graphics processing, audio-video enhancement, fast algorithm implementations and rapid numeric processing applications. DSPs are essentially fast number-crunchers. Their features include which high speed-to-size performance, comparatively low-cost and low-power consumption. DSP features include providing ADC functionality and fast processing, as explained below. Data and Control signals on Wireless carriers are in analog form, and they need to be converted to digital mode to treat the information discontinuously, as a discrete series of binary numbers. The goal of digital signal processing is to use the power of digital computation to manage and modify the signal data. Therefore, the first stage in many DSP systems is to translate smooth real-world signals into a digital approximation. This translation is accomplished by an Analog-to-Digital Converter (ADC). After successful and complete translation, the data points give a detailed and accurate rendering of the signal. After removing irrelevant frequencies, the ADC passes its digitized signal information to a DSP, which does the bulk of the processing. Eventually, after signal processing and ‘conditioning’ the digital data may be turned back into an analog signal, albeit one that is quite different from and much improved over the original.
In Wireless domain, DSP filters the noise from a baseband signal, remove unwanted interference from Wireless carrier, amplify audio and baseband frequencies and suppress others, encrypt (For example, Scramble cellular phone conversations to protect privacy) or decrypt information using algorithms and techniques, or analyze a complex wave form into its spectral components for Wireless carriers. Basically, digital signal processing is highly numerical and very repetitive and the primary challenge is the speed requirement for DSP systems to work in real time, capturing and processing information as it happens. In Wireless devices and systems, ADCs and DSPs must keep up with the work flow. If they fall behind, information is lost and the signal gets distorted. For example, in Wireless devices or units, ADC must fetch the signal samples fast enough to catch all the relevant fluctuations. Imagine trying to record a 2-minute video of a ‘Live’ football game with a GPRS mobile phone (with inbuilt camera) running at one frame per second. If the ADC isn’t fast enough, the film would be incoherent, missing entire plays in the intervals between frames. The DSP must also keep up the pace, computing out calculations as fast as the signal data is received from ADC. While playing digital audio (Polyphonic ringtones, MP3 files, FM Radio) on your mobile phone, the stereo equipment handles sound signals of up to 20 kilohertz (20,000 cycles per second, the upper limit of human hearing), requiring a DSP to perform hundreds of millions of operations per second. In case of satellite phones, the signal from satellite transmissions are even faster, reaching up into the Gigahertz (billions of cycles per second) range!

DSP Processors (DSPs)
DSP devices are often differentiated based on small to large calculations that are processed for the application. Generally the processor’s capacity is based on the size of data it can handle for processing and the type of arithmetic computations it is capable of DSP Processors used in applications like telecommunications and wireless units are generally 16-bit, 24-bit, 32-bit. Needless to say 32-bit processor has a wider dynamic range as compared to others. Similarly two types of arithmetic computation which DSPs can handle are fixed point and floating point, where the latter has a higher dynamic range. The System Designer can decide on which processor will be best suitable for the application where the DSPs will be applicable.

Some of the examples include:

Application

DSPs preferred

Reasons

Wireless units / Cell phones (Voice only)

16-bit fixed-point

Works on relatively narrow range of sound frequencies

Mobile units / Cell phones with in-built MP3 player

24-bit fixed-point with 16-bit or 24-bit ADC

Hi-fidelity stereo sound with wider range

Mobile units / Cell phones with in-built camera to capture still pictures and video in color

32-bit floating-point

Much greater dynamic range for image processing, high quality gaming

DSP in Wireless environment
There are many constraints for wireless devices and systems which fall into consideration, like low power design and power control, when we consider the signal processing aspects. Wireless is an area where DSP plays a very important role, especially in the field of baseband processing and even microprocessing.Wireless Signal Processing is extensively included in systems like GPS, CDMA, WLAN, Multimedia Messaging, etc. Multimedia Messaging includes a potential area of DSP, i.e. Image Processing, Audio and Video Processing. Nowadays, all newly launched cellular and mobile phones are Multimedia enabled. By the year end 2005, the global percentage of multimedia-enabled phone users is expected to grow above 90%.

How DSP and Communication System Application areas combine to provide DSP Application areas in Wireless Communication
Digital Signal Processing :Coding, Compression and Information extraction. Digital Signal Processing, Image Processing, Stochastic Processes, Pattern Recognition, Speech Processing, Algorithms for Signal Processing, Object Remote Sensing, Digital Communication and Neural Networks
Communication Systems Application areas :Wireless Communication Systems, Satellite Communication Systems, Spread Spectrum, Cellular Systems, Digital Communication Systems, Analog Communication Systems, Data Communications Microwave Systems, Antennas and others.
DSP Application areas in Wireless Communications
Telecommunications – Protocol signaling & interfacing,
Speech – Codecs (e.g.
EFR for GSM, EVRC for CDMA),
Image and Video Processing – JPEG, JPEG2000 for 3G phones, MPEG3 and MPEG4 for 2.5G & 3G phones,
Digital Audio – DTMF processing, Polyphonic ringtones on Cellular and Mobile phones, MP3 Audio processing,
Consumer – DSP Processor Cores for Cellular and Mobile phones, Games and Web Access using Multimedia phones, Camera-enabled phones,
Space – Satellite Communication, GPS phones and mobile devices

As a DSP Engineer, following user requirements are of importance for DSP design considerations –
Long Battery life and Low Power consumption
Lesser charging time
Sound clarity from headphone and to microphone
Accurate processing of Video signals for enjoyable viewing
Clarity in digital audio tone/ sound
Uninterruptable connectivity with Cellular or Mobile Networks
Faster Time-bound Processing of DSP Processor


RF Issues for Wireless Systems
Wireless personal and mobile cellular communications are expected to be one of the hottest growth areas of 2000 and beyond. They have enjoyed the fastest growth in the telecommunications industry – adding customers at a rate of 20-30% globally in the Area of Wireless communications, a year. Presently, at least six satellite systems are being developed so that personal voice and data communications can be transmitted from any part of the earth to another using a simple, handheld device. These future systems will provide data and voice communications to anywhere in the world, using a combination of wireless telephones, wireless modems, terrestrial cellular telephones and satellite phones. The use of wireless remote sensing, remote identification, direct broadcast, global navigation and compact sensors has also gained popularity in the past decade. Wireless communications and sensors have become a part of consumer’s daily life. All of these wireless systems consist of a radio frequency (RF) or microwave front end.

Antennas for Wireless Communications – Sounds Obvious!
From mobile telephones to wireless Internet access to networked appliances and peripherals, there is an increasing reliance on wireless communications to provide or enhance functionality for products and services. The wireless communications industry continues to generate new products and applications for consumers and new opportunities for businesses. The enormity of the opportunities presented by the current explosion of wireless applications is accompanied by comparable design and manufacturing challenges.
The world of wireless communications can appear to be a confusing offering of services, products and standards, all competing for dominance in a dynamic marketplace. But regardless of modulation, protocol, bandwidth or frequency, every wireless device requires an antenna for transmission and/or reception.
The antenna is often taken for granted, but its performance is critical to the successful operation of any wireless system. Three major areas of activity in antenna research and development have emerged to meet the needs of modern communications systems: size reduction, wideband or multi-band operation, and adaptive pattern control.

Now, we shall look into the following topics which are considered mainly while designing a Wireless Device or Unit –

[ Wireless Signal Processing Algorithms for Modulation, Equalization and Encryption ]
[ High Performance DSPs and Dynamic Programming Algorithms ]
  a. High Performance DSP – Techniques and Processors
  b. Dynamic Programming Algorithms for Viterbi, Turbo and Reed-Solomon Codes
[ Power Control – Design and Techniques ]
  a. Low Power Design Strategies for Wireless Devices
   b.Power Control Techniques in Wireless Systems
[ Signal Processing in CDMA ]
[ Signal Processing in GPS ]
[ Signal Processing in OFDM for 802.11 (Wireless LAN) ]
[ Multimedia Signal Processing Algorithms for Image, Audio (Codecs) and Video for  Mobile devices ]
[ RF and Baseband Signal Processing in Wireless Units ]
[ Antenna Design and Analysis for Wireless Devices and Networks ]

 


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