Voice over Wireless LAN via IEEE 802.16 Wireless MAN and IEEE 802.11 Wireless Distribution System *

Today, IEEE 802.11 Wireless LANs (WLAN) have been widely deployed to provide wireless broadband access in local areas such as campuses or offices. Most of the WLANs are connected to the backbone via a wired distribution system (DS). IEEE 802.16 Wireless MANs (WMAN) aim to extend the wireless broadband access up to kilometers to facilitate the long-range “last-mile ” solution. For short-range extension, IEEE 802.11 Wireless Distribution System (WDS) can be set up easily by connecting Access Points (AP) together to form multi-hop networks. This provides a quick, easy and low-cost solution up to hundreds meters. In this paper, we exam the capacity challenges in delivering voice traffic over WLANs which are connected to 1) IEEE 802.16 WMAN and 2) IEEE 802.11 WDS. For 1), we show that the capacity is limited by the WLAN bottleneck and we propose a multiplex-multicast (M-M) scheme [1] to double the capacity. For 2), we show that the M-M scheme should also be adopted in WDS. This scheme can sufficiently improve the voice capacity up to 7 times (from 3 to 22 voice sessions) in a 4-hop WDS. To verify our simulation results in [2], we set up a real multi-hop WDS. Experimental measurements confirm that our proposed scheme can increase both the voice capacity and service coverage of WDS. 1. Background Conventional VoIP scheme transmits packets to/from each client individually over the wireless * This work was sponsored by the Areas of Excellence schem

A wavelength switchable passively harmonically mode-locked fiber laser with low pumping threshold using single-walled carbon nanotubes

We propose and demonstrate a wavelength switchable passively harmonically mode-locked fiber laser with low pumping threshold using single-walled carbon nanotubes (SWCNT). When the pumping power of 980 nm laser diode is 60 mW, passive mode-locking (PML) of a soliton erbium doped fiber laser at the 23rd harmonic of fundamental cavity frequency is experimentally observed at the central wavelength of 1530 nm. By only adjusting the polarization of laser in the cavity, another PML at the 13th harmonic is successfully achieved at 1554 nm. The supermode suppression (SMS) of each wavelength is larger than 30 dB. The pulses at 1530 nm are characterized in details with a repetition rate of 328.44 MHz, a transform-limited pulse width of 1.3 ps, and a timing jitter of 142.6 fs.Accepted versio