Tuesday, January 31, 2012

Hack Patriot Box Office for Watching Chinese Videos and TVs

As requested by friends, this blog is dedicated to explain a simple way for watching Chinese TV programs and movies on a television or monitor for free using a special media player instead of a computer.  Compared with many well-known approaches watching Chinese TVs on a computer, this one seems much more operation-friendly as well as eco-friendly.  It is attractive for many Chinese families who may not always be technical savvy.  In addition, as I know, the operation cost or power consumption of this kind of MIPS-based media players is relatively low.  Its total power consumption usually is no more than 15 watts.  Meanwhile, a typical power consumption of a PC CPU, even some mobile or laptop CPUs,  itself is known to be between 50 watts and 100 watts.  Even a power efficient Intel Atom CPU usually is inside a range between 5 and 20 watts, as I remember.  Nowadays a typical home desktop demands a power supply of no less than 250 watts, not to mention that a powerful game desktop or work station easily require a power supply of at least 400 watts.

The media player which I am introducing here is a Patriot Box Office High-Definition Media Player PCMPBO25 which a Realtek RTD1073DD SoC based networked player and made by Patriot Memory.  It has about 128MB SPI flash, 128MB DDR2 SDRAM and a 400MHz MIPS core.  One nice thing about this player is Patriot Memory hosts a very OPEN and friendly support forum for it and shares a lot of details of its firmware.  This not only makes this player hard to be bricked but also enables many mods and hacks.  One simple mod I am going to introduce here is to update its firmware for watching Chinese movies and TV programs.

The procedure for updating its firmware has been posted on Patriot Memory support forum.  Now, it is slightly modified and reposted here for your convenience.
  1. Watch over composite hookup if possible ( Comment: Though I have hacked many PBOs with watching over HDMI without any issues so far, YMMV);
  2. Download firmware;
  3. Unzip/unrar;
  4. Copy "install.img" file to the ROOT directory of an FAT32 FORMATTED USB drive ONLY;
  5. Put the USB drive into the front usb port of Patriot Box Office;
  6. Power up both PBO and TV and choose the PBO input on TV menu;
  8. The screen will black out for about a few seconds until the update process initiates. The whole update process may reboot & resume, please DO NOT remove the usb drive UNTIL the screen goes back to the setup page; and
  9. (Optional) Additional update might be necessary if the remote doesn't work after the above update.
As far as I know, the newest unofficial firmware supporting China videos, movies and TVs is the one posted on HDP Fans Forum [11/2011].

Friday, January 20, 2012

What Is The Next for Mobile System Design? I: A Single-Cell Model Perspective on Downlinks

Interference Cancellation: A Short Overview
How to Broadcast Multimedia Contents?

[Note] Due to the asymmetry between the uplinks and downlinks of a mobile network, there are different considerations, tradeoffs and techniques for designing each directions. In general, with the recent advance on uplink interference cancellation and management techniques, mobile network is usually limited by downlinks due inter-cell interference, especially when delay is a key part of the equation. On this blog, my focus will be on downlinks. How to evolve mobile system uplinks will be discussed in separated blogs.

Mobile system design usually starts from our understanding of wireless channels and the services customers are demanding. The properties of various wireless channels can help us understand the system design limitation we are facing and the potentials we may achieve.  For example, COST 231 model, which was developed by European COST Action 231. Its variations are the most popular radio propagation models used in almost every wireless standardization body, including 3GPP, 3GPP2 and IEEE. Its modifications include COST 231-Hata Model and COST 231-Walfisch-Ikegami Model. One nice thing of COST 231 channel model is it helps us understand the tradeoff between reception and coverage we are facing in a typical single-cell environment.
Figure 1. Spectral Efficiency and Coverage Tradeoff

As shown in Figure 1, with a 300-meter-tall transmitter antenna, we can see that the path-loss changes 0.66 dB at every 90% coverage change, 1.39 dB at every 80% coverage change, 2.22 dB at every 70% coverage change and 3.18 dB at every 60% coverage change. In general, if you want more coverage, then you may lose some capacity especially on the cell-edge.  Otherwise, you have to shrink your coverage.

Figure 2.  What we want to achieve.
As shown in Figure 2, though there is a fundamental tradeoff between coverage and performance we are constantly facing in our system design, customers always desire their mobile network having both better coverage and higher performance for less. Now the challenge to us is how to push up the system design boundary. There are at least three major approaches available to push the envelope. They are 1) interference cancellation and management, 2) multi-antenna technology and 3) cells cooperation and relay.

Figure 3.  Mobile System Design Options
Interference cancellation (IC) and management are the key ingredients for mobile network to achieve optimal performance. There are many ways to do interference cancellation, linear ICs (decorrelating detector, MMSE IC) and Nolinear ICs (joint detection, decision feedback IC ). Interference management can be done in time, frequency and space domain. OFDMA-liked multiplexing scheme is friendly to interference management.  MIMO can help meet the demand of high data rate and high link quality. It can not only help improve link quality through spatial diversity and beamforming but also help achieve higher data  throughput using spatial multiplexing and multiuser MIMO. The third weapon is heterogeneous transmission and deployment, which can help improve the network throughput as well as cell-edge user experience. Cooperation between cells is not something very new. Starting from 2G/IS-95, there has been soft handoff for macro-diversity. Additionally in 3G, we did it for broadcast multicase service over mobile networks, e.g., CDMA2000 BCMCS or UMTS MBS. However, all these cell cooperations are coordinated by MSC.  More recently, LTE-Advanced standardized X2 interface between eNodeBs belonging to the same MME.  This makes neighboring cells cooperation, such as corrdinated multi-point transmission and reception (CoMP), inter-cell interference coordination (ICIC) and relay, a reality. Similarly in CDMA2000 EV-DO Rev. C, there is a feature called single-carrier multi-link (SCML), which essentially extends the capability of multi-carrier devices in a single-carrier environment.