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Issues and Challenges
High performance usually requires power sacrifices. The objective is to find the perfect balance between the two within a particular design. Optimize for performance when speed is an absolute must and target everything else for low power. There are a number of design and process strategies for achieving economical performance at system-level, chip-level, and even transistor-level designs, to achieve performance with long battery life.
Closing the Technology Gaps
Figure 1 summarizes the key challenges facing the mobile device industry. The step function labeled 1G, 2G, 3G, and 4G depicts the gains in cellular transmission over time. This follows
Figure 1. Key Technology Gaps [1]
Shannon's law that predicts two times the transmission performance improvement in 8.5 months. Given Moore's law, it takes semiconductor manufacturers 18 months to double the number of transistors and therefore double the microprocessor performance. In addition, it takes battery makers 5 to 10 years to achieve comparable increase in power density. Also memory access time performance doubles every 12 years.
The gaps define the challenges faced by the mobile device industry. They include:
- Microprocessor and memory bandwidth gap
- Power reduction gap
- Algorithmic complexity gap
These gaps are the major hurdles to successful commercialization of mobile devices. In order to provide the advanced features and services required in future networks, system performance, as predicted by Shannon's law of Algorithm Complexity, must improve at a rate faster than Moore's law without compromising power budgets.
This has traditionally been tackled in the mobile device by making each instruction more efficient or executing multiple instructions at the same time. The increasing size of the
Shannon-Moore gap with time means that incremental transistors and MHz alone are not sufficient to close this gap.
Always On, Always Connected: Paradox of the Portable Age
These "palm" size, portable devices that free people to go anywhere anytime also keeps them tethered by electrical power cords, plugs, and sockets. Sophisticated devices with multimode radios, color displays, 3D audio, video, and gaming features demand more from batteries without recharging. Users plunge from being always in touch to feeling impotent.
Users of portable devices have become "socket seekers." Strategically seeking out positions in airports, hotels, conference rooms, and home close enough to electrical sockets allowing one to recharge your portable devices.
The cycle of renewing battery life has introduced new rituals. Power strips are fully occupied with portable devices similar to animals feeding at a trough. Handheld and cell phones go into their cradles before you retire for the evening to bed. The digital cameras and iPod play musical chairs on the wall sockets. Commute time becomes critical charge time.
Well-dressed professionals can be found sitting next to whatever needs to be charged. Road warriors carry bags full of chargers. It is the most important and least talked about problem in consumer electronics.
Each year batteries become more powerful and circuitry improvements make devices more efficient. However, batteries cannot keep up with the rising expectations for longer life.
Balancing Battery Life with Performance and Cost
Mobile consumers have become accustomed to the size, weight, cost, and battery life of voice-only devices. New product offerings will be measured against these existing metrics, regardless of what new features they offer. Any noticeable regression from the current voice-only level could impact adoption on new data-centric devices. A mobile device that provides high speed data requires greater computing power and greater RF power consumption, resulting in shorter battery life.
In that respect, every technology has specific power requirements impacting battery life. Improvements in battery technology will enhance all radio access technologies, so that the differences between how current technologies use battery power are likely to persist for some time.
Figure 2 shows a comparison of the peak mobile power dissipation while transmitting for the different technologies. The values include both digital processing and RF elements.
Figure 2. Power Consumption of Cellular Technologies
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