Power Allocation in Multitone Systems
- Reference: T98012
| Description | Filename | Size | Download |
|---|---|---|---|
| Brochure | T98012-069.pdf | 512,212 KB | Download |
Benefits
- Enables higher data rates: The algorithm can achieve the highest data rate for a given channel's SNR characteristics.
- Reduces error rates: The algorithm can minimize the probability of error for a given data rate.
- Fits emerging technologies: The algorithm is compatible with one new wireless standard and several emerging DSL standards.
- Affords flexibility: The user can choose whether to optimize data rate or error probability.
- Eliminates added equipment costs: No requirement for increases in hardware or software costs.
Applications
- Wireline broadband protocols: DSL and other OFDM protocols
- Wireless and fixed wireless protocols: including 802.11A.
Details
This technology provides a method for allocating power among several channels in multichannel, orthogonal frequency division multiplexed systems. It improves achievable data rates or signal-to-noise ratios and reduces errors in transmission. One type of OFDM system uses discrete multitone protocol, which includes all asymmetrical digital subscriber line (ADSL) systems and residential DSL systems; however, the algorithm can be used with any OFDM system where the SNR varies across channels.
How It Works
Power in a communications channel is limited, usually by regulations (FCC, telephony laws, etc.), to prevent interference with other devices or for safety reasons. This limits the amount of power that a system can put out, forcing the communications industry to trade off between data rate, signal-to-noise ratio, and transmission power. If transmission power is increased, SNR increases as well, resulting in a better signal and the capability to send more data on the signal.
The signal also can be improved if it is broken up into individual subchannels. In some systems, all subchannels would have roughly the same SNR, and the same data or error rate could be achieved on each subchannel. However, in other systems, such as OFDM systems, the quality of each signal can be individually improved. OFDM splits the signal into several frequency channels, allowing the characteristics of each channel to be optimized, yielding better results than simply averaging the data rate over the whole channel. Dealing with the channels individually enables the full capacity of the channel to be approached, attaining the best possible data rate with no error.
Although it treats channels individually and divides the power among them, the algorithm ties them together, so as not to exceed the total power limit. The algorithm uses information on SNR, data rate, and other parameters to allocate power to either (a) achieve the best data rate for a channel's given SNR characteristics or (b) minimize the probability of error for the specific data rate by altering the SNR. The user can choose to optimize one way or the other, depending on the system and its constraints.
Why It Is Better
This technology optimizes with greater efficiency and speed than other optimization methods (e.g., Hughes Hartog method) at speeds comparable to the ad hoc methods currently used but which are less efficient. It provides a simple way to achieve the theoretical maximum power allocation with no added cost in hardware or software.
The algorithm can be used in wireless systems to maximize the channel capacity in frequency-selective fading situations, where the channel stays stable for tens of OFDM data blocks.
Since the trend in high data rate communications standards is toward OFDM, and most new technologies are OFDM-based, this technology is timely and appropriate.
