Mohd,

For your "packetization protocol" needs, you could take a look at HDLC. As a data link standard, it is quite encompassing and is the base protocol that many other protocols are derived from. The standard defines many different classes of operation. Some classes specify a complex connection-oriented protocol with error detection and correction through retransmission. On the other extreme complexity-wise, some classes specify a connectionless protocol that only has a framing component with error detection. Many commercial RF subsystems use the "high end" HDLC classes to present an error-free RF link mechanism to the "user". On very low end 8051 and PIC projects, I use the simple connectionless class and define a dirt-simple RPC-like upper-layer protocol that has the "superior" (often PC) end of the link responsible for requesting any retransmission rather hand having the "inferior" (MCU) end of the link manage it.

Your post did not state a need for DC-balancing, but since Manchester has been brought up, I'll throw the time-tested 4B/5B NRZI balanced encoding scheme into the mix. Manchester encodes one bit into two physical layer "bits", whereas 4B/5B encodes four bits into five physical layer "bits" while still providing transitions for clock recovery if you need it.

4B/5B expands a 4-bit symbol (nibble) into a 5-bit symbol leaving 16 "out of band" symbols. A subset of these remaining symbols have been given special meanings and functions. For example 'I' (IDLE) causes the physical layer to transition every bit and the ordered pair "JK" (SYNC0, SYNC1) present themselves on the physical layer in a manner that will never appear in the data itself. "IIJK" is a great preamble and SYNC pattern. You can map HDLC's starting FS (flag sequence) to the JK ordered pair and the ending FS to the 'T' (TERM) symbol.

Any of the 16 "out of band" symbols that you elect not to use, can serve to enhance error detection (in addition to your CRC). For example, let's say you have defined your symbol set to be the obvious 5B_0 through 5B_F, IDLE, the two SYNC symbols, and 'T' (TERM) to terminate the data stream. That leaves 12 out of 32 symbols that if received, are a "code violation". If you get a code violation, you have detected an error before you even got the end of the transmitted frame.

Anyway, I have used 4B/5B for the physical layer encoding on countless low-cost, low-power RF projects with great success. It provides better bandwidth utilization and more "functionality" than some alternatives.