Information for Request for NPRM

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Information for Request for Rules Change Title: Release from APC Requirement for Spread Spectrum Operation Under Part 97 of the FCC Rules Introduction: The following is rational for petitioning the FCC for Release from Automatic Power Control (APC) for stations operating Spread Spectrum under Part 97 of the FCC Rules. It is a well documented fact that the "hidden transmitter" affect can be extremely detrimental to any RF network. This extends from an unheard station on 20 meters to a hidden packet station operating on 2 meters. This same problem exist when operating IEEE 802.11b on 2.4 GHz. The hidden transmitter or station can cause collisions to such an extent to "bring down" the entire network. IEEE 802.11b Standard Operation: The basic access method for 802.11 is the Distribution Coordination Function (DCF) which uses Carrier Sense Multiple Access / Collision Avoidance (CSMA/CA). This requires each station or node to listen to other users. If the frequency/channel is idle, the node may transmit. However, if the channel is busy, each station waits until transmissions stop and then the node enters into a random back off process. This process prevents multiple nodes from seizing the channel immediately after completion of the preceding transmission. Packet reception in DCF requires acknowledgment (ACK). The period between the completion of the packet transmission and the start of the ACK is a short Inter Frame Space (SIFS). ACK frames have a higher priority than other frames. Fast ACKs is one of the important features of the IEEE 802.11b standard because it required ACKs to be handled at the MAC level. Transmissions other than ACKs must wait at least one DCF inter frame space (DIFS) before transmitting data. If a transmitter senses a busy channel, it determines a random back-off period by setting an internal timer to an integer number of slot times. Upon expiration of a DIFS, the timer begins to decrement. If the timer reaches zero and the station may begin transmitting. However, if the channel is "seized" by another station before the timer reaches zero, the timer setting is retained and the decremented value for subsequent transmissions. The above relies on the "Physical Carrier Sense." The underlying assumption is that every node can "HEAR" all other stations. This is not always the case. To combat cases where all or most of the stations are unable to hear each other, a second carrier sense mechanism is available. "Virtual Carrier Sense" enables a node to be able to reserve the channel for a specified period of time through the use of Request to Send (RTS) / Clear to Send (CTS) frames. In the case described above, a node sends an RTS frame to an access point (AP). The RTS may not be heard by another node unless it is running sufficient power. If this case, one node cannot hear the other node. The RTS frame contains a duration/ID field which specifies the period of time for which the channel is reserved for subsequent transmissions. The reservation information is stored in the Network Allocation Vector (NAV) of all stations detecting the RTS frame. Upon receipt of the RTS, the AP responds with a CTS frame which also contains a duration/ID field specifying the period of time for which the channel is reserved. Even though a node did not detect the RTS, it will detect the CTS and update the NAV. Thus, collisions are avoided even though some nodes are hidden from other nodes. Point Coordination Function (PCF) provides contention-free services. Special stations called point coordinators are used to ensure that the medium is provided without contention. Point coordinators reside in access points (APs), so the is restricted to infrastructure networks. To gain priority over standard contention-based services, the PCF allows stations to transmit frames after a shorter interval. The PCF is not widely implemented in current IEEE 802.11b hardware. Rational for not using APC: While the above provides a high level of protection against collisions from hidden transmitters (nodes); however, it assumes that the AP can hear all stations. In the ARRL 802.11b environment, this may not be true. In many instances, there will be a AP node located considerably higher than other nodes and the AP node that acts as a gateway to the Internet or other network services may not be heard by other network nodes. Additionally, in ARRL 802.11b network operation it is reasonable to assume that in some large area WLANs, the only node that a member node can hear is the AP repeater node located at a considerable height above the ground. In this instances, the AP repeater node must transmit sufficient power so that all network nodes can hear every transmission it makes and cannot afford to negotiate automatic power control. Many, if not most, links (distance between network stations) in ARRL 802.11b networks will be a considerable distance apart. Distances between stations can be from one half a mile to 7 to 20 miles. This is considerably further than manufacturers of 802.11b hardware anticipate. Network analysis tools indicate that at these greater distances, the radiated power needs to be between 2 and 10 watts with normal receiver sensitivity and using gain antennas in the 9 to 15 db range. With 802.11b, the better the signal to noise ratio the higher the speed throughput. It is as simple as that! The further you are away from an 802.11b AP or other node, the lower your signal to noise ratio will be and the lower your data rate throughput will be. Recent field experiments by Dr. John Champa, K8OCL, reveled that everywhere on a three acre tract, he could connect to the AP at 11 Mbps. The AP had a simple external, outside, antenna. As he moved about one half mile from the AP, using only a laptop's integrated antenna, the data rate dropped to only 1 Mbps. This clearly shows that 802.11b operating is a lot closer conceptually to what we think about signal strength, i.e., the more you have is generally better, within reason and good operating practices. The use of power output above one watt without APC will insure that the effects of the hidden transmitter are minimized and insurance of high data throughput. Requested Action by the FCC: The FCC is requested to increase the requirement for Automatic Power Control above one watt for Spread Spectrum Operation as required in Part 97.311(d) to 10 watts. Prepared by: Walt DuBose/K5YFW Member, ARRL HSMM WG 25 Jan 2003

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Information for Request for Rules Change

Title:
Release from APC Requirement for Spread Spectrum Operation Under Part 97 of the FCC Rules

Introduction:
The following is rational for petitioning the FCC for Release from Automatic Power Control (APC) for stations operating Spread Spectrum under Part 97 of the FCC Rules.

It is a well documented fact that the "hidden transmitter" affect can be extremely detrimental to any RF network. This extends from an unheard station on 20 meters to a hidden packet station operating on 2 meters. This same problem exist when operating IEEE 802.11b on 2.4 GHz. The hidden transmitter or station can cause collisions to such an extent to "bring down" the entire network.

IEEE 802.11b Standard Operation:
The basic access method for 802.11 is the Distribution Coordination Function (DCF) which uses Carrier Sense Multiple Access / Collision Avoidance (CSMA/CA). This requires each station or node to listen to other users. If the frequency/channel is idle, the node may transmit. However, if the channel is busy, each station waits until transmissions stop and then the node enters into a random back off process. This process prevents multiple nodes from seizing the channel immediately after completion of the preceding transmission.

Packet reception in DCF requires acknowledgment (ACK). The period between the completion of the packet transmission and the start of the ACK is a short Inter Frame Space (SIFS). ACK frames have a higher priority than other frames. Fast ACKs is one of the important features of the IEEE 802.11b standard because it required ACKs to be handled at the MAC level.

Transmissions other than ACKs must wait at least one DCF inter frame space (DIFS) before transmitting data. If a transmitter senses a busy channel, it determines a random back-off period by setting an internal timer to an integer number of slot times. Upon expiration of a DIFS, the timer begins to decrement. If the timer reaches zero and the station may begin transmitting. However, if the channel is "seized" by another station before the timer reaches zero, the timer setting is retained and the decremented value for subsequent transmissions.

The above relies on the "Physical Carrier Sense." The underlying assumption is that every node can "HEAR" all other stations. This is not always the case. To combat cases where all or most of the stations are unable to hear each other, a second carrier sense mechanism is available.

"Virtual Carrier Sense" enables a node to be able to reserve the channel for a specified period of time through the use of Request to Send (RTS) / Clear to Send (CTS) frames. In the case described above, a node sends an RTS frame to an access point (AP). The RTS may not be heard by another node unless it is running sufficient power. If this case, one node cannot hear the other node. The RTS frame contains a duration/ID field which specifies the period of time for which the channel is reserved for subsequent transmissions. The reservation information is stored in the Network Allocation Vector (NAV) of all stations detecting the RTS frame.

Upon receipt of the RTS, the AP responds with a CTS frame which also contains a duration/ID field specifying the period of time for which the channel is reserved. Even though a node did not detect the RTS, it will detect the CTS and update the NAV. Thus, collisions are avoided even though some nodes are hidden from other nodes.

Point Coordination Function (PCF) provides contention-free services. Special stations called point coordinators are used to ensure that the medium is provided without contention. Point coordinators reside in access points (APs), so the is restricted to infrastructure networks. To gain priority over standard contention-based services, the PCF allows stations to transmit frames after a shorter interval. The PCF is not widely implemented in current IEEE 802.11b hardware.

Rational for not using APC:
While the above provides a high level of protection against collisions from hidden transmitters (nodes); however, it assumes that the AP can hear all stations. In the ARRL 802.11b environment, this may not be true. In many instances, there will be a AP node located considerably higher than other nodes and the AP node that acts as a gateway to the Internet or other network services may not be heard by other network nodes.

Additionally, in ARRL 802.11b network operation it is reasonable to assume that in some large area WLANs, the only node that a member node can hear is the AP repeater node located at a considerable height above the ground. In this instances, the AP repeater node must transmit sufficient power so that all network nodes can hear every transmission it makes and cannot afford to negotiate automatic power control.

Many, if not most, links (distance between network stations) in ARRL 802.11b networks will be a considerable distance apart. Distances between stations can be from one half a mile to 7 to 20 miles. This is considerably further than manufacturers of 802.11b hardware anticipate. Network analysis tools indicate that at these greater distances, the radiated power needs to be between 2 and 10 watts with normal receiver sensitivity and using gain antennas in the 9 to 15 db range.

With 802.11b, the better the signal to noise ratio the higher the speed throughput. It is as simple as that! The further you are away from an 802.11b AP or other node, the lower your signal to noise ratio will be and the lower your data rate throughput will be.

Recent field experiments by Dr. John Champa, K8OCL, reveled that everywhere on a three acre tract, he could connect to the AP at 11 Mbps. The AP had a simple external, outside, antenna. As he moved about one half mile from the AP, using only a laptop's integrated antenna, the data rate dropped to only 1 Mbps.

This clearly shows that 802.11b operating is a lot closer conceptually to what we think about signal strength, i.e., the more you have is generally better, within reason and good operating practices.

The use of power output above one watt without APC will insure that the effects of the hidden transmitter are minimized and insurance of high data throughput.

Requested Action by the FCC:
The FCC is requested to increase the requirement for Automatic Power Control above one watt for Spread Spectrum Operation as required in Part 97.311(d) to 10 watts.

Prepared by:
Walt DuBose/K5YFW
Member, ARRL HSMM WG
25 Jan 2003