Building Unicode Database

I have a problem with Insert and Update Unicode data to database
I can send Unicode data using string with N prefix (Ref 001)

Below I write some line of my SP
But It does not write Unicode data to table, it writes like ????????
How to insert data using n prefix with Declared Variable?
How can avoid this problem?
Any other method to pass unicode data using SP?
Please help me...

column UnitName nvarchar

Sample Stored Procedure (SP)
SP header:

CREATE PROCEDURE ltrsp_AddEditUnit
@UnitID char(4),
@UnitName nvarchar(20),
@UtrID int

Insert:

INSERT INTO ltrtb_Unit (UnitID,UnitName,UtrID) VALUES (@UnitID,@UnitName,@UtrID)

Update:
---
UPDATE
ltrtb_Unit
SET
UnitName=@UnitName, UtrID=@UtrID

WHERE
UnitID=@UnitID



Ref 001:

found a method to insert unicode data to table (Using N' prefix), but I want to add using declared variable

INSERT INTO ltrtb_UserLevel (UserLevel,Description) VALUES (1,N'Unicode String')
From the URL,
http://databases.aspfaq.com/general/why-do-some-sql-strings-have-an-n-prefix.html

But I need to know how to pass the data using stored procedure