Subject: [manet] why cs_thresh is 10dB lower than rx_thre

From: lining_nj <[email-masked]>
Date: Tue, 27 Aug 2002 15:55:04 +0800

Hello everybody,
    In GloMoSim & NS, the default carrier sensing threshold is both 10dB lower than receiving threshold. But in my simulation(use GloMoSim), there are 100 stationary nodes randomly distribute in a 1000m*1000m terrain. There are 100 1-hop flows, I use 802.11 MAC protocol, RX-SNR-THRESHOLD is set to be 6dB,RADIO-TX-POWER 24.5dBm,RADIO-RX-THRESHOLD -64.0dBm.I use different RADIO-RX-SENSITIVITY from -78.0dBm to -64dBm.
    The results show that, the higher the carrier sensing threshold, the bigger the total network throughput. 
    If the results are correct, I wonder why the carrier sensing threshold is usually set 10dB or more lower than receiving threshold? Are there any hardware related resons? 
Thanks in advance
Ning Li.

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From: Nael Abu-Ghazaleh <[email-masked]>
Date: Wed, 28 Aug 2002 16:29:12 -0400 (EDT)

Hi--

RTS/CTS is not effective for nodes that are outside the reception
range; these nodes can still generate enough power to interfere at
the receiver.  So, the carrier sense threshold is chosen to be low enough
to prevent many (most?) of the nodes that are in interference range
(but not in reception range) from interfering with an ongoing
communication.  Not a perfect solution.

regards,
-nael
---
Dr. Nael Abu-Ghazaleh
Assistant Professor -- CS Dept. 
State University of New York
Binghamton, NY 13902--6000
(607) 777 4748 (Phone)
(607) 777 4729 (Fax)
[email-masked]

On Tue, 27 Aug 2002, lining_nj wrote:

> Hello everybody,
>     In GloMoSim & NS, the default carrier sensing threshold is both 10dB
lower than receiving threshold. But in my simulation(use GloMoSim), there
are 100 stationary nodes randomly distribute in a 1000m*1000m
terrain. There are 100 1-hop flows, I use 802.11 MAC protocol,
RX-SNR-THRESHOLD is set to be 6dB,RADIO-TX-POWER
24.5dBm,RADIO-RX-THRESHOLD -64.0dBm.I use different RADIO-RX-SENSITIVITY
from -78.0dBm to -64dBm.       
>     If the results are correct, I wonder why the carrier sensing
threshold is usually set 10dB or more lower than receiving threshold? Are
there any hardware related resons?

---

From: Nael Abu-Ghazaleh <[email-masked]>
Date: Wed, 28 Aug 2002 16:29:12 -0400 (EDT)

Hi--

regards,
-nael
---
Dr. Nael Abu-Ghazaleh

---

From: "Zhenqiang(Frank) Ye" <[email-masked]>
Date: Wed, 28 Aug 2002 13:50:44 -0700 (PDT)

Hi, Ning Li:
  By increasing the carrier sensing threshold, you can decrease the
interference range of a node, thus you can get some frequency reuse
benefits.

Frank

---

From: "Zhenqiang(Frank) Ye" <[email-masked]>
Date: Wed, 28 Aug 2002 13:50:44 -0700 (PDT)

Hi, Ning Li:

Frank