5. Is UWB Best Technology for WPAN?

5.1 Next Generation WPAN Performance Requirement and UWB Technology

Before Discussing about the next generation WPAN performance requirements a few words are in order in order to make clear the difference between WPAN and WLAN standards. These two technologies are separately defined and governed by different technical specifications, standards, and industry alliances. For instance , WPAN standards have been developed by the IEEE 802.15 working group while the WLAN standards have been developed by the IEEE802.11 working group. Typically, WLAN offer greater range while WPANs feature higher throughput and lower power.
WPANs products are currently enjoying good market success, and next generation WPANs solutions(such as Bluetooth's Seattle Release) look to increase data rates in order to handle additional applications such as short range streaming video. New Functionalities and storage capabilities are regularly being added to portable devices, which is driving the need for fast wireless connectivity. The main application today for new WPANs is file transfer , but a more interesting emerging application is streaming video.
Because it requires continues periods of high bandwidth consumption in order to provide a good user experience, streaming video is a unique application. Its maximum throughput requirement ranges from 8Mbps for 320* 240 video resolution to 200Mbps for 2048*1024 video resolution. Compromising on throughput or bandwidth would likely make this application unsuitable.
UWB is the obvious choice to enable these new high-bandwidth applications becouse its key feature is high throughput at short ranges, which is precisely what WPANs require. For this reason, both the Bluetooth SIG and the USB_IF have selected UWB for next-generation WPANs
In order to be used as a Bluetooth Alternate MAC/PHY , WiMedia UWB ( one of the groups discussed in section 4) meets the following requirements( table 5.1):

• Throughput..........................greater than 100Mbps
• Power Consumption..........1mW/Mbps
• Operating frequency..........Above 6GHz

5.2 Which is better for WPAN....IEEE802.11 or UWB?

There are several types of WLANs on the market,and all based on a different type of IEEE 802.11 standards: 802.11a, b, and g are widely deployed today and the draft 2.0 802.11n is currently being fielded. The newer 802.11n has received much press on its promise to enable higher data-rate and longer range wireless networking applications. Indoor ranges for 802.11n are expected to reach up to 70 meters , and outdoor ranges may approach 160 meters. Without doubt this is a clear advancement in WLAN performance in terms of throughput and range.This performance improvement , however , comes with a necessary increase in power consumption and cost because it requires multiple radio chains (Multiple Input Multiple Output MIMO technology).
Because of 802.11's success in WLANs , some are thinking of using the same technology in the next generation of short-range WPAN applications. The WiMedia Alliance ( one of the special interest groups in the UWB Technology) explains why UWB is the best technology for WPAN.
They Compare UWB technology with 802.11n interims of:

• Performance
1. Throughput
2. Power Consumption
• Interference
1. to Bluetooth
2. to Wi-Fi
3. to WiMAX
   
• Cost

a. Performance

1. Throughput: recent testing has shown that, without interferers, 802.11n actually achieves throughputs of 20 to 100Mbps, while 802.11g achieves 25Mbs. WiMedia UWB products today can achieve up to 377Mbps.

2. Power Consumption: This is one of the most important requirements for WPANs because they are intended for use with portable, battery-operated devices. To be successful in the market place,next-generation WPANs must be optimized for low power consumption in order to satisfy consumer expectations. Table below gives the power/Mbps of the different technologies.


As can be seen from the table UWB has low power consumption. This is because UWB systems have been designed for low power consumption from the beginning, taking advantage of the low transmit power allowed by the regulatory rules for this technology.


b. Interference

One of the main applications of next-generation WPAN will be Video streaming, which requires the radios to use large amounts of spectrum, as I already mentioned before. Because of this , next-generation WPANs need to provide some level of spectrum planning in order to avoid interference. If an 802.11 radio is used( instead of an UWB one ) for WPAN, then there are at least three risks of interference caused by the 802.11 radio to other applications in the 2.4 GHz range.This is due to current 802.11 systems considered for WPAN operate in the 2.4GHz range.

1. Interferenceto Bluetooth: In recognition of the risk from WLAN radios, specific mechanisms have been adopted in the latest versions of the Bluetooth specifications to combat interference caused by 802.11 Wi-Fi. Now, a Bluetooth radio can avoid certain channels that are being used by a nearby Wi-Fi radio at specific times. This Technique would be much less efficient, and likely fail, if an 802.11 radio were being used for WPAN video streaming applications ( These streaming application transmit most of the time, which would leave little opportunity for Bluetooth operation.)
2. Interference to Wi-Fi : WI-Fi systems are very successfully used in homes and offices to provide wireless internet access. The bursty nature of the traffic characteristic of internet access allows a large number of users to share the same 2.4 GHz spectrum. Using 802.11 radios for WPANs will cause the 2.4GHz spectrum to be much more crowded, and it is likely to cause serious performance degradation for existing WLANs.
3. Interference to WiMAX: UWB transmitters operating at 3.1GHz or above meet the WiMax required emission ( -70dBm/MHz) , but the 802.11 emission of -41dBm/MHz is much higher than the maximum allowable emission for WiMAX . Obviously UWB transmitters operating above 6GHz exceed that limit by a large amount.

C. Cost
Unit cost for 802.11g is low enough to enable high volume applications.Most manufacturers integrate a majority of the radio components (with exception of power amplifiers) in a single CMOS IC. The same is true for UWB, where multiple companies have demonstrate highly-integrated single-chip CMOS implementations. On the other hand, 802.11n implementations are still expensive and currently ship for four times as much as their 802.11g or UWB counterparts. It is reasonable to expect that the cost of 802.11n will eventually be reduced to 2* that of 802.11g because they include, at minimum, two or more radios.

5.3 Summery and Final Remarks:
The Table below summarizes how the different technologies compare for WPAN applications.







It is clear that 802.11 is optimized for WLAN, because it performs at much higher range than required by WPAN , at higher power, and the cost of 802.11n is too high for WPAN applications. The interface from 802.11 to WIMAX is also a problem when used for stream video.
Observing the current performance of the technologies, the best alternative, may be,is to continue using 802.11 for its intended purpose-WLAN- and use UWB for WPAN. UWB has the distinct advantage of operating at much lower transmit power levels in the 3.1GHz to 10.6GHz ranges, which is well out of the range of WI-Fi, WIMAX, AND Bluetooth 2.0 signals. Implementing UWB technology in WPAN systems avoids all of the interference problems that plague WLAN.